Do pitch counts count?

For the past two weeks, we’ve been looking at whether certain types of pitchers age better than others. We started with Bill James’ contention that pitchers with high strikeout totals age better and pitch longer than do comparable pitchers with low strikeout totals; we found the evidence to be inconclusive. Then we looked at a couple of other theories, and found that pitchers with low walk totals seem to age a lot better than equally good pitchers with high walk totals. This week, we’ll tie up a few loose ends.

A bunch of readers have been clamoring for a better understanding of how the pitchers we’re looking at compare in all the relevant statistical categories, so I’ll start by printing the fielding-independent lines for each group of pitchers:

                Before age 26           After age 26
            SO/9    BB/9    HR/9    SO/9    BB/9    HR/9
High-K      8.43    3.99    1.03    7.69    3.29    1.04
Low-K       5.61    2.89    0.89    5.53    2.76    0.98

High-BB     7.95    4.22    0.92    7.32    3.60    0.99
Low-BB      6.16    2.57    1.00    6.11    2.53    1.02

We can make a few general observations from looking at this table. First, there are a lot of similarities before age 26 between the high-strikeout and high-walk pitchers and between the low-strikeout and low-walk pitchers. The high-strikeout and high-walk pitchers have both high strikeout rates and high walk rates, and the low-strikeout and low-walk pitchers have both low strikeout rates and low walk rates. All the groups have fairly average home run numbers, though the high-walk and low-strikeout groups are a bit better at a young age.

Second, we can see that the high-strikeout and high-walk groups become a bit less extreme as they age—the high-strikeout pitchers strike out many fewer hitters after turning 26 (while also walking fewer batters), and the high-walk pitchers issue many fewer free passes (while also getting fewer strikeouts). By contrast, the low-strikeout and low-walk groups keep pretty much the same statistical lines, though the home run rate for low-strikeout pitchers does go up a bit.

Take from these numbers what you may. What I find most interesting is that pitchers with high walk totals seem to improve their control as they get older, but this improvement is offset by a decrease in strikeouts. Overall, improved control does not appear to increase their innings pitched later in their career compared to pitchers who started off with low walk totals.

But let’s move on. One theory I found particularly interesting was posited by Guy in the Ballhype comments to my last article. Guy wondered whether the low-walk pitchers actually fared better than did the high-walk pitchers, and proposed that we might not have found such an effect because the low-walk pitchers had longer careers, and therefore longer decline phases. In other words, the question is whether having a low walk rate means not only more innings pitched in the future but also better performance.

To avoid the decline phase, Guy suggested that we look at each group’s later performance only from ages 26 to 31, and figure out whether that might be the case. Now let’s recall that, before turning 26, the high-walk pitchers had a Fielding Independent ERA (FIP) of 4.41, whereas the low-walk pitchers had a FIP of 4.34. And between 26 and 31? The high-walk pitchers stayed at 4.41, while the low-walk pitchers posted a 4.32.

In other words, both groups performed at exactly the same level between the ages of 26 and 31 as before. Unfortunately, then, we must reject Guy’s theory—when it comes to their effectiveness, high-walk and low-walk pitchers seem to age in the same way.

There is one more theory that I want to check out before we (hopefully) wrap up this topic. That is a theory that I kind of hastily tossed out at the end of my last article in trying to explain why low-walk pitchers seem to last so much longer than their high-walk counterparts. Although I did not have any certain explanation, it was my suspicion that this durability might have something to do with pitch counts.

High-walk pitchers, of course, are forced to expend a lot more effort to get through an inning. Since I had built my groups so that the high-walk pitchers had the same number of innings pitched before the age of 26 as did their low-walk counterparts, I guessed that the high-walk pitchers would have much higher pitch counts at that point. And indeed they did, throwing an estimated 12,045 pitches before turning 26 versus an estimated 11,358 pitches for the low-walk pitchers.

But what does that difference mean? Do the low-walk pitchers last longer because they’ve less wear on their arms, or is it something else? We can use regression here to try to tease out the answer, though frankly, it is somewhat of a rough tool. Specifically, we can try to predict the number of innings that a pitcher will throw after turning 26 based on the number of innings that he threw before age 26 along with his pre-26 strikeout rate, walk rate, FIP, and pitch count. And this time, we can use our entire database of pitchers with at least 500 innings pitched by age 26.

What kind of results do we get? Here you go:

          Coefficient  P-value
Intercept   994.195     0.246
SO/9         50.251     0.324
BB/9        129.112     0.213
FIP_ERA    -272.288     0.065
<26_IP        9.195     0.002
<26_Pitch    -0.547     0.004

Only the last three coefficients are actually significant. Some of the results are obvious. Pitchers with higher FIP ERAs to age 26 pitch fewer innings in the future, because they aren’t very good pitchers. Also, those with high innings pitched totals early throw many more innings later, probably because they are very good and durable.

But what stands out most is that, after controlling for all these other variables, every pitch thrown before age 26 knocks off half an inning in the latter half of a pitcher’s career. That is a pretty huge effect. Consider, 100 extra pitches a year—just three pitches a start—means 55 fewer innings pitched down the road.

The other thing that jumps out is that, once we control for all these variables, neither walk rate nor strikeout rate seem to have a significant impact on a pitcher’s future durability. As I said, regression is an imperfect tool, and this evidence is not incontrovertible; nonetheless, based on the evidence we have seen, it does not appear that either skill has much effect on how long a pitcher lasts.

What does seem to have an effect is pitch counts. How and why—well, that’s a whole other story.