Diving into the Intentional Walk

By: Collin Kannenberg, Ben Stockton, Khyam Paneru


“An intentional walk occurs when the defending team elects to walk a batter on purpose, putting him on first base instead of letting him try to hit. Intentional walks — which count as a walk for the hitter and a walk allowed by the pitcher — are an important strategy in the context of a game. They can be used to put a runner on first base, setting up a potential double play” (Intentional). An intentional walk in baseball occurs when the pitcher deliberately throws four unhittable pitches to put the batter on first base.  In March 2017, MLB altered the rule to disallow the pitcher from throwing the four pitches and instead required the manager to signal to the umpire that they wanted the hitter walked.  The main purpose of this rule change, according to Commissioner Rob Manfred, is to speed up the game.  He issued a statement at the time of the change saying, “We don’t think that that particular change — we know how the math works — is going to have a momentous impact on the game. By the same token, every little change that makes the game faster, I personally believe is a good thing for the game over the long haul.” (DeFranks)  MLB believes shortening the game time by reducing downtime will keep young fans interested in the game, but is disallowing the pitcher to throw the four pitches really a necessary change given the possible effects on the game?  The average time of an intentional walk could be estimated, however, since there is little strategy in those four pitches, the plate appearances should not be very long.  As a result of enacting this rule to save time, MLB may assume that because unusual events, such as a wild pitch or a hit, occur very rarely during an intentional walk attempt, it is a waste of a minute. This is compounded by the infrequent use of intentional walks.

MLB has focused mostly on the reduction of time and less on the impact on the players. It is commonly believed that pitcher’s performance is dependent on their rhythm of motion.  During innings where the offense is performing well and the half inning is lasting longer than normal, the pitcher will begin stretching in the dugout to ensure he is ready for pitching.  Another example of rhythm effecting a pitcher is during rain delays when a manager would rather bring in a fresh pitcher after the starter pitched only a couple innings.  Those are large scale examples compared to how only four pitches can effect rhythm, but the principle is the same: a pitcher’s rhythm is important to his performance.  Phil Rosengren of betterpitching.com is a former pro pitcher and current pitching coach states the following about a pitcher who has lost his rhythm, “Then on the next pitch, they slow things down in an effort to control their mechanics. All this does is disrupt the natural flow of momentum, killing velocity and actually hurting their control”(Rosengren).  In this study, an in-depth analysis of outcomes of the plate appearance immediately following intentional walks in 2016 and 2017 will be conducted.  Factors such as the velocity of the following pitch, horizontal and vertical movement of the following pitch, and other pitching metrics listed below will be analyzed in this study.  This study will give a more definite answer to whether the four-pitch intentional walk was worth eliminating from the game.

Table : Variables

Variable Description Values
Year Season in which the plate appearance occurred. 2016, 2017
Balls The amount of balls in the count when an event (ball put in play, strikeout, or walk) occurs. 1-4
Strikes The amount of strikes in the count when an event (ball put in play, strikeout, or walk) occurs. 1-3
First Pitch The first pitch of the plate appearance. Ball or strike
Velocity (MPH) Velocity of the first pitch thrown following the intentional walk
Pitch Type The type of pitch thrown after the intentional walk FF(4-seam fastball)

FT(2-seam fastball)






Horizontal Movement (In.) How much the pitch moves horizontally from the pitcher to home plate.
Vertical Movement (In.) How much the pitch moves vertically from the pitcher to home plate.
Average Velocity (MPH) For each pitchers’ data collected in the random sample, their season average velocity of same pitch they threw following the intentional walk was collected.
Average Horizontal Movement (In.) The pitchers’ average horizontal movement on the pitch over the course of the season.
Average Vertical Movement (In.) The pitchers’ average vertical movement on the pitch over the course of the season.



The purpose of tracking balls and strikes in the count until an event occurs is to determine any difference in both the hitters’ approach and the pitchers’ command.  Specifically, would a pitcher be behind in the count when an event occurred.  In the analysis, tracking first pitch strikes also helps estimate the pitchers’ command and if his command has an impact on the result of the plate appearance.  Studies (cited in Fangraphs later in the article) have shown that pitchers tend to have more success when they throw a first pitch strike.  Velocity  helps determine if the pitchers generally throw their first pitch following an intentional walk slower or faster than they normally throw that same type of pitch.  Just as essential to velocity is movement, so a significant change in horizontal or vertical movement is just as important as a change in velocity. The average pitch velocity of the same type of pitch as thrown by the same pitcher was obtained from Fangraphs’ pitch info data and was used for the average horizontal and vertical movements of the pitches. Collecting season averages is important for analyzing residualsData was collected for all plate appearances immediately following intentional walks.  Obtained was a random sample of 277 plate appearances in 2016 when pitchers had to throw the four pitches, and 277 plate appearances in 2017 when managers signaled the intentional walk instead of throwing the pitches.  Only plate appearances following an intentional walk where the pitcher had to throw at least 3 balls intentionally were in the sample.  In the case where the pitcher tried to get the batter to chase out of the zone but and then decided after two balls to throw two more intentional balls to walk the batter, that data was omitted.  The random sample of 277 plate appearances is representative of a full season.  By using the

Considering the volume of intentional walks over the course of the season, there is question as to how much of an impact this rule change will have due to the small number of intentional walks.  The quantity of intentional walks per year has been declining steadily since 2012 and is a rare plate appearance result.

Figure 1: Number of Intentional Walks Past 6 Seasons

After the rule change, more intentional walks were issued.  It is important to note the pitch distribution between seasons in this sample is similar since the analysis is comparing the two seasons.

Figure 2: Distribution of Pitches 2016 and 2017

When Intentional Walks Are Thrown:

If a pitcher is intentionally putting a batter on base, there are most likely extenuating circumstances.  It would be expected that intentional walks occur in high leverage points of games.

Figure 3: Number of Intentional Walks by Inning 2016 and 2017

It can be observed from the plot that as the game progresses, more intentional walks are thrown up until the 9th inning.  The most common inning in which to throw an intentional walk remained the 8th inning.  While total number of intentional walks in the 8th inning decreased from 2016 to 2017, there was an uptick in intentional walks nearly every other inning in 2017.


In terms of velocity, the batter will not necessarily find it more difficult to hit a 96-mph fastball than an 98-mph fastball. To the hitter, both pitches are incredibly fast and they most likely would not be able to tell the difference.  A change in velocity could be an indicator if the pitcher is out rhythm.  If a pitcher is consistently throwing 97 mph fastballs and then lobs four pitches at around 50 mph, the next fastball might be 94 or 95 mph instead of the average of 97 mph.  In 2017, we expect the pitcher not to vary too much from his seasonal average.

The results of the Welch two sample t-test:

2016 and 2017 Velocity with Season Averages
2016 Residuals 2017 Residuals 2016 to 2017
4-Seam Fastball 0.01 0.32 0.08
2-Seam Fastball 0.28 0.91 0.25
Changeup 0.68 0.97 0.21
Curveball 0.39 0.81 0.63
Slider 0.04 0.49 0.65
Sinker 0.39 0.68 0.66
Cutter 0.91 0.56 0.53

Table 1: Velocity T-tests Results

2016 and 2017 Horizontal Movement with Season Averages
2016 Residuals 2017 Residuals 2016 to 2017
4-Seam Fastball 0.99 0.004 0.001
2-Seam Fastball 0.732 0.129 0.854
Changeup 0.902 0.984 0.783
Curveball 0.517 0.529 0.008
Slider 0.475 0.812 0.798
Sinker 0.92 0.719 0.745
Cutter 0.635 0.383 0.979

This t-test is used to compare the average means of each pitch’s velocity from 2016 to 2017.  While it is included in this analysis, it is important to note the league-wide increase in velocity from 2016 to 2017 that has nothing to do with intentional walks.  The primary interest lies in observing how first pitches following intentional walks compare to the average velocity from that year as documented in the first and second coll.  Another t-test comparing the 2016 pitch velocities to the 2016 season’s average of the pitch was also analyzed in addition to in 2017.



Fangraphs definition of horizontal movement in the horizontal movement section shows the type of lateral movement each pitch gains on average (fangraphs).  Individually, horizontal movement does not determine the effectiveness of the pitch.  Other factors such as location and velocity play significant roles in the pitch outcome.  The magnitude of horizontal movement depends on the type of pitch.  Cutters will have more horizontal movement than a four-seam fastball or a changeup.  The following chart displays the p-values for the t-tests of each pitch by right handed and left-handed pitchers

16 LHP Residuals 17 LHP Residuals 16 RHP Residuals 17 RHP Residuals
4-Seam Fastball 0.98 0.12 0.82 0.7
2-Seam Fastball 0.71 0.6 0.42 0.37
Changeup 0.97 0.82 0.5 0.46
Curveball 0.87 0.22 0.33 0.81
Slider 0.37 0.11 0.73 0.49
Cutter 0.71 0.42 0.6 0.37

Table 2: Horizontal Movement T-test Results

There is no statistically significant difference in horizontal movement compared to average horizontal movement within years for both 2016 and 2017.

Vertical movement  is the up or down movement of the pitch relative to a pitch with no spin.  A pitch cannot defy gravity and move up.  Alan Nathan, physicist at University of Illinois-Urbana Champaign, defines vertical movement as follows, “Movement is the deviation of the trajectory from a straight line with the effect of gravity removed.” (Nathan) A ball with more backspin will have less downward movement compared to a ball with less backspin.  Vertical movement is included in this analysis to observe if the pitcher has lost some sharpness on his pitch.  A pitcher out of his rhythm might throw more flat sliders and curveballs than usual.

There is a significant difference in the total vertical movement among the sample (p<.001).  In 2017 pitchers had significantly more vertical movement on their pitches.  The following table shows the results of the t-tests when breaking down vertical movement by pitch:

2016 and 2017 Vertical Movement with Season Averages
2016 Residuals 2017 Residuals 2016 to 2017
4-Seam Fastball 0.99 0.004 0.001
2-Seam Fastball 0.732 0.129 0.854
Changeup 0.902 0.984 0.783
Curveball 0.517 0.529 0.008
Slider 0.475 0.812 0.798
Sinker 0.92 0.719 0.745
Cutter 0.635 0.383 0.979

Table 3: Vertical Movement T-test Results

There is a significant difference in the total vertical movement between the four seam fastballs thrown in 2016 to the four seam fastballs thrown in 2017.  There has been an increase in vertical movement in 2017.  In 2017, when a pitcher threw a four-seam fastball immediately following an intentional walk, the vertical movement was significantly greater than the average fastball movement throughout the season.  Considering that there was no significant difference from the average velocity of a four-seam fastball in 2017 while there was a significant difference in 2016, we can conclude that a four-seam fastball thrown right after an intentional walk is both and shows more life than the four seam fastballs thrown after an intentional walk in 2016.

First Pitch Strike:   

Pitchers never want to get down in the count.  It puts the pitcher at a disadvantage as they will have to attack the strike zone giving the hitter something to hit.  First pitch strikes are incredibly important, and is really the most important part of this study to see if a pitcher who had to throw the 4 intentional balls will end up coming back and starting the next batter off with a strike.  Many studies have been done on the importance of pitchers getting ahead in the count.  In a Hardball Times article on first pitch strikes, Craig Burley notes, “92.7% of the time, if you throw a strike to the opposing hitter, you get either a 0-1 count or an out.” (Burley).  When the first pitch is accounted for, a 0-0 strike produces a hitters’ line of .261/.296/.411 compared to an 0-0 ball where the hitters line is .280/.385/.459 (Burley).  This is a substantial difference.

Figure 4: First Pitch Strike Following an Intentional Walk 2016 and 2017

In 2016 pitchers threw a first pitch strike following an intentional walk 57% of the time compared to 2017 when pitchers threw a first pitch strike 67% of the time.  When performing a t-test, this is a statistically significant change at the .1 rejection level (p=0.068). This is strong evidence that at least for the first season, eliminating the four-pitch intentional walk does impact the outcome of the following plate appearance.


Regardless of vertical or horizontal movement a pitcher has on a pitch, or the velocity at which it is thrown, location of the pitch is the most important pitch attribute.  For instance, a 94 mph fastball low and outside appears slower than that same pitch high and in on the hitter.  This is called effective velocity.  Scott Spratt of Fangraphs defines effective velocity as, “the theory of Effective Velocity is that the location of the pitch influences how the batter perceives the velocity of the pitch.” (Spratt) As more research comes out on this topic, the more effective velocity is understood to be  an important characteristic of a pitch.  Command of a pitch is a difficult aspect of pitching to quantify since some pitches are meant to be down in the dirt or not where the catcher is setting his target.   As an example, we will take 3 pitchers who intentionally walked a batter on August 21, 2017 and plot their pitches following the intentional walk:

Figure 5: Pitches thrown after an IBB on 8/21/2017

These pitches are all out of the zone.  We also plot the rest of the pitches that those pitchers threw throughout the rest of the game.

Figure 6: All other pitches of the same type thrown the rest of the game

It can be observed, for example, how after Justin Verlander intentionally walked a batter, his next pitch, which was a fastball, was far out of the strike-zone.  Compare this to the plot that shows the rest of the fastballs he threw that game, and it can be noticed that he never missed that far out of the zone in that location.  While no conclusions can be drawn from this, it shows that a top-tier pitcher can maybe lose his momentum due to an intentional walk.  There are other factors such as where the catcher was setting up, but it may not be a coincidence that his only fastball misses that far low and away (for a RHB) was the pitch directly after the signal for an intentional walk.  That is just one example in a small sample from one day out of the season.  In 2017, it is expected that there are less of the Justin Verlander-like cases than in 2016.  Much of the other pitches stay consistent with the location of the pitches those pitchers threw during the rest of the game.  Verlander was the only big deviation.

Using Pitch F/x data, we plotted all the pitches in all the zones outside of the strike zone and all the pitches within the strike zone.  This provided the most accurate description of what was a strike or not.  There may be some error regarding the zone as a players’ size may differ and the way the home plate umpire calls the game may vary. Plot of accompanying zone percentage for every pitch following an intentional walk in 2016:

Figure 7: Zone Percentage of Pitches Following IBBs 2016

This next plot illustrates all the balls and strikes following an intentional in the date range in 2017 using Pitchf/x location.

Figure 8: Zone Percentage of Pitches Following IBBs 2017

In comparing the zone percentage, we notice that in 2017 the zone percentage is about 2 percentage points better than in 2016.  When looking at season zone rates from baseballreference.com, the season total for a first pitch is 60.2% in 2017 and 60.1% in 2016.  Compare that to every first pitch thrown after an intentional walk, there is a much more significant increase in zone percentage. It increases by nearly 2 percentage points in pitches after the intentional walk compared to .1 of a percentage point when looking at season totals.


Other Metrics:


The Big Picture

After examining the data for 2016 and 2017, significant changes can be seen, but what overall effect does this have?


2017 Run Expectancy Chart
Runners Exp_R_Outs_0 Exp_R_Outs_1 Exp_R_Outs_2
000 0.52 0.29 0.11
003 1.36 0.93 0.38
020 1.11 0.69 0.33
023 1.95 1.33 0.6
100 0.89 0.54 0.23
103 1.73 1.19 0.51
120 1.48 0.94 0.46
123 2.32 1.59 0.73

Source: Baseball Prospectus


The table for 2016 is very similar.  As an example, the 3rd line indicates a runner on 2nd base and going across is the expected runs that inning with 0,1, and 2 outs.  Therefore, with a runner on 2nd base and 1 out, the batting team is expected to score .6899 runs.  The change in a first pitch strike rate will change the run expectancy.  Since the sample sizes are very similar with 930 intentional walks in 2016 and 968 in 2017 the two seasons can be compared easily.  The most common occurrences of intentional walks in 2017 was with 2 outs and a runner on 2nd base.  Suppose that a pitcher intentionally walks a batter in that situation.  The expected runs that inning goes from .3298 to .4553.  Now the pitcher needs to face the next batter with maybe a bit more of his rhythm than he would have in 2016.  Considering that there is a significant increase in first pitch strike percentage of about 2 percentage points, the batter following the intentional walk is more likely to start down 0-1 in the count.  The difference, though, is minute.  Considering a season of 1000 intentional walks, there will be about 20 more first pitch strikes following the intentional walk than there would be in 2016.  Batters have an on-base percentage of .283 in 0-1 counts and their on-base percentage increases to .385 when ahead in the count 1-0.  With 20 more plate appearances starting in 0-1 counts, it would be predicted that around 5 batters would reach base instead of 7 when the hitter is ahead in the count 1-0 assuming only the first pitch strike data and all else remaining constant.  Overall, throughout the course of an entire season the impact is minimal.  However, given the high leverage situations in which intentional walks occur, this could result an extra win or loss for a team.  This could in turn effect the standings late in the regular season for teams, or the result of a playoff game.


Works Cited


Burley, Craig. “The Importance Of Strike One (Part One).” The Hardball Times, 11 Oct. 2004, www.fangraphs.com/tht/the-importance-of-strike-one-part-one/.


DeFranks, Matthew. “New Intentional Walk Rule to Be Implemented Soon, Manfred Says.” SunSentinel, 28 Feb. 2017, www.sun-sentinel.com/sports/miami-marlins/fl-sp-mlb-manfred-rule-changes-20170228-story.html.

“Intentional Walk (IBB).” MLB.com, 2018 MLB Advanced Media, m.mlb.com/glossary/standard-stats/intentional-walk.

Nathan, Alan M. “Determining Pitch Movement from PITCHf/x Data .” Http://Baseball.physics.illinois.edu, 21 Oct. 2012, baseball.physics.illinois.edu/Movement.pdf.

Rosengren, Phil. “Pitching Principle # 3: Tempo.” BetterPitching.com, 7 Oct. 2017, betterpitching.com/pitching-principle-3-tempo/.

Spratt, Scott. “Effective Velocity Disciples.” Fangraphs.com, 13 Apr. 2017, www.fangraphs.com/fantasy/effective-velocity-disciples/.

Leave a Reply

Your email address will not be published. Required fields are marked *