In Search of the Veteran Benefit of the Doubt, Part Two

A little earlier, I played around with some strike-zone data. There’s a theory out there that umpires are more willing to give veteran pitchers the benefit of the doubt when it comes to called strikes. I wanted to investigate that, and sure enough, I was able to turn up a modest effect related to age and experience. However, my suspicion is that this has less to do with doubt benefits, and more to do with pitcher command. It makes sense that more experienced pitchers would be better command pitchers, and it makes sense that better command pitchers would end up with a little called-strike benefit given what we understand about good and bad pitch-framing, and so on. It’s something that could be investigated further, and I’ll think of what I did as a simple starting point.

Now, if we’re going to look at pitchers, we should also look at hitters. Just as there’s a theory that veteran pitchers get the benefit of the doubt, there’s also a theory that veteran hitters get the benefit of the doubt, in the opposite direction. In short, a lot of people believe that umpires are biased in favor of age and experience. I don’t know where this comes from, but enough people have repeated it that it’s worth a quick look with the numbers we have available. Once again, what follows isn’t exhaustive, but once again, it should get us started. If there’s any kind of major effect, this study should be able to find it.

The methodology is all the same as before. It leans on season-to-season PITCHf/x data from 2008 through 2013. Based on what we have here, we know how many strikes hitters have seen. Based on what we have here, we know how many strikes hitters should have seen. As with pitchers, for the sake of consistency, I’m going with Diff/100, which roughly corresponds to the difference between strikes and expected strikes per 100 innings, relative to the league average. It’s awkward to use an innings denominator when looking at hitters, but it’s also awkward to force a plate-appearance denominator since different hitters can have such different approaches. For the average hitter, the denominator is equivalent to a little more than 400 trips to the plate. I’m just going with Diff/100 so the numbers can be easily compared to the numbers for the pitchers.

You’re going to see data for five groups, for each of the last six years:

1. rookies
2. hitters up to 25 years old
3. hitters aged 26-30
4. hitters aged 31-35
5. hitters at least 36 years old

Rookies have accounted for about 13% of plate appearances. The elders have accounted for about 7%. Players 26-30 have accounted for about 45%, making for the most highly-represented sample. Rookies, incidentally, have struck out 2.8 times for each walk, while the elders have struck out 1.9 times for each walk. That ought to surprise no one.

An important point: for pitchers, a positive Diff/100 is good, because it means more strikes than expected. For hitters, a positive Diff/100 is bad, for the same reason. A positive Diff/100 suggests a bigger called strike zone, which works to the hitter’s detriment. If the theory about veteran hitters were to hold true, we’d expect younger hitters to show a more positive Diff/100 than older hitters. Here, now, is all the information.

Group	2008	2009	2010	2011	2012	2013	Average
Rookies	4.5	4.2	8.0	5.1	7.5	6.2	5.9
Through 25	4.2	4.5	6.9	3.8	4.4	5.3	4.9
26-30	1.9	-0.6	2.5	-1.2	0.1	1.2	0.6
31-35	-1.0	-2.4	-3.9	-3.6	-0.8	-2.2	-2.3
36+	-7.3	-4.5	-8.8	-0.6	-5.9	-3.8	-5.2

And there you go. As with the table for pitchers, the most important column is the last one, which averages the previous six. And as with the table for pitchers, this table for hitters shows something of a trend that correlates with age. Rookies have gotten more strikes than expected. The oldest hitters have gotten fewer strikes than expected. There’s a small decrease with each successive group. The effect, again, is relatively small, but at least it looks like there could be something there.

What the table suggests is that veterans have gotten the benefit of the doubt, compared to younger hitters. To only a very small extent, however. The difference between rookies and guys 36+ is about one extra strike per 79 called pitches. The difference between rookies and guys 31-35 is about one extra strike per 107 called pitches. On average, there are about 2.1 called pitches per plate appearance, so the shown difference between rookies and guys 36+ would be about one strike per 38 trips, or about 16 strikes per 600 trips. That works out to a difference of about two runs, over a full season. That’s comparing either extreme.

And now for the alternate hypothesis. I think the explanation for the trend with pitchers is that older pitchers have better command. Hitters, of course, don’t have “command” in the same sense, but I wouldn’t be surprised if this were related to discipline. While hitters can’t control where the pitches are going, guys can have different commands of their zones, and perhaps with experience hitters become more able to adapt to the strike zones as they’re called. This analysis treats all pitches in the zone as equals, and all pitches out of the zone as equals. Veteran hitters might lay off pitches less likely to be called strikes. Younger hitters might swing at a different distribution of pitches that would only really reveal itself through a deeper PITCHf/x analysis. Again, this is a starting point.

I started out investigating whether veteran hitters get the benefit of the doubt from home-plate umpires with regard to the called strike zone. The data is more supportive of the hypothesis than non-supportive. That said, there could be an alternate explanation that once more has to do with a kind of survivor bias. And regardless of the explanation, the observed effect is so small as to be imperceptible over a given plate appearance, or even over a stretch of them. It might well be that veteran hitters are treated a little more nicely than inexperienced hitters, overall as a group, but when it comes to any given controversial ball or strike call, the call presumably would’ve been made because of something else.