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Walks, Strikeouts and Pitch Counts

Several pitchers like Max Scherzer, Brandon Morrow and Danny Duffy have struggled with control this season. Each has thrown a ton of pitches resulting in both walks and strikeouts. The number of pitches they have thrown has limited the amount of innings they are able to pitch in a game. By limiting the number of pitches thrown per batter, a pitcher will end up increasing the number of innings pitched over an entire season.

Many pitchers take a quite a few pitches to get through a game. The main causes for more pitches is a high number of strikeouts and walks. Each of these events take a certain number of pitches, 3 or 4 at minimum, for the event to happen. A pitcher that walks and strikes out 3 batters an inning will not allow any runs to score. Each of these innings will take 21 pitches to get through. The problem is that they will only throw 5 to 6 innings since the pitcher will be at 100 pitches near the beginning of the 5th inning. Depending on the pitcher’s pitch count limit, they will not even make to the 6th inning to qualify for a quality start.

Here are 4 pitchers from this season with 31 starts and have near the same number of pitches per game (data was taken last week so some of the number may have changed):

Name % K and BB IP Pitches per Batter Pitches per Game
Ryan Dempster 31.1% 183.2 4.00 102.6
Max Scherzer 27.3% 184.1 3.99 101.6
Luke Hochevar 22.8% 198.0 3.73 100.6
Randy Wolf 22.2% 200.2 3.74 102.3

Each pitcher averages just bit over 100 pitches per start. Hochevar and Wolf have less walks and strikes outs and average less pitches per batter than Dempster and Scherzer. The difference can further be seen in a 15 inning difference in IP this season from the 2 groups.

With these observations, I looked at the effects of strikeouts and walks on IP. I found a decent correlation between the number of walks and strikeouts when compared to pitches per batter (r-sqaured = 0.50) and pitches per IP (r-sqaured = 0.30). The final equation I ended up feeling comfortable with was:

Pitches/IP = 7.626 (K%) + 15.678 BB% + 13.518

Basically, pitchers averaged 13.5 pitches per inning and those numbers changed as the number of strikeouts and walks increased or decreased. Walks have twice the effect on pitches per batter than strikeouts. I expected to see the walk rate be a bit higher because of the extra pitch for a walk vice A strikeout. The doubling effect on pitches thrown shows how important it is to throw strikes.

Using the equation, here is the number of IP per season for a pitcher depending on the pitch limit they are on. The league average values (18% for the K% and 7.5% for the BB%) are used. The results of increasing or decreasing each value 2% is also shown.

BB% K% 120 P/G 110 P/G 100 P/G
7.5% 18.0% 239.0 219.1 199.2
5.5% 18.0% 243.8 223.4 203.1
9.5% 18.0% 234.4 214.9 195.4
7.5% 16.0% 241.3 221.2 201.1
7.5% 20.0% 236.8 217.0 197.3

The main item that sticks out is that small changes don’t make that much of a difference over the season. A change in BB% by 2% changes the total by only 4 IP. Not all changes are so small as seen in the 4 pitchers I looked at earlier. Here is the number of IP that they would have been predicted throw over 31 starts and 100 IP given their K% and BB%:

Name IP Season IP Predicted
Ryan Dempster 186.1 183.2
Max Scherzer 190.7 184.1
Luke Hochevar 194.9 198.0
Randy Wolf 193.3 200.2

The predicted difference is not as much as the actual difference, but it is a measurable difference.

Pitchers that have high pitch counts from walks and strikeouts will see an effect on the number innings they are able to throw. Over an entire season the difference could end up being the equivalent of two extra games worth of IP.