Every year, around this time, players advertise themselves as being in the best shape of their lives, either because their offseason conditioning regimens improved, or because previously they were lazy. I think the players are almost always being sincere ā they probably, genuinely, feel great ā but as fans, we identify this as a cliche, and we generally dismiss it. For one thing, we hear this claim entirely too often. For another, itās never been demonstrated that thereās a relationship between best shape and on-field success. Or, if you prefer, on-field improvement. Itās been studied, albeit not exhaustively so.
Thereās something particular I want to examine, though, and it has to do with Jhonny Peralta. This is an article about Peralta from Friday morning. Within:
Fewer pounds would be preferable, they told him, as he headed home for the winter. He got the message and lost 18.
āItās good,ā Peralta said. āIāve never been at this weight since Iāve been with Detroit. I finished last season at 236. Iām at 218 now.ā
āDombrowski and everybody wanted me working on my range,ā he said. āThatās why I tried to get lighter. So I can be quicker, especially up the middle.ā
Itās funny ā everyone, a year ago, was prepared for the Tigersā infield defense to be dreadful, what with having Prince Fielder and Miguel Cabrera at the corners. It was pretty bad, especially if you ask Rick Porcello (off the record). But at least according to the numbers, Jhonny Peralta was fine. DRS characterizes him as being about a league-average defensive shortstop. UZR characterizes him as being an above-average defensive shortstop. People talk about Peraltaās limited range, but overall, it doesnāt seem like thereās much to complain about. But we can proceed anyway.
Peralta wants to get better at defense, so he says he lost weight. A pretty significant amount of weight, for that matter, and he says he lost it in a healthy way. Itās intuitive how weight loss and better conditioning could make a defender improve. But I was curious whether we could find anything in the numbers if we looked at previous examples. So I pulled up some previous examples.
I identified 16 players who, between 2011 and 2012, claimed to have lost at least ten pounds. They lost this weight on purpose, and it wasnāt because they were ill or anything. I wanted to know what happened with their defense, so I put their season-before and season-after Fld + Pos numbers over a denominator of 1,000 innings. In this way, I get UZR, and I also account for changes in position. A year ago, did weight loss lead to defensive improvement?
Welp. Hard to get less meaningful than that. Some players got better, and some players got worse, but, overall, there was virtually no change within the group. What they were, defensively, in 2011, they were again defensively in 2012.
Now for the caveats. For one thing, you know about the issues with UZR. For another thing, you know about the issues with a small sample size. And what we donāt know is what these players wouldāve done in 2012 if they hadnāt lost weight and trained as they did. We donāt have a control, so it could be that the -3.0 post-loss average is significant. All the players got a year older, and as players get older, defense declines. As a group, the defense didnāt decline, so thatās of interest. But we definitely donāt see a strong effect. If thereās a benefit, weāre talking about a very small handful of runs, probably.
Something to consider is the somewhat arbitrary nature of reporting baseball player weight. Itās not always listed accurately, and sometimes players report weight loss from the previous spring, while sometimes they report weight loss from the end of the year. Additionally, offseason conditioning matters only so much ā all players train in spring training, and then weight can change over the course of the regular season. A player whoās lost, say, 15 pounds come the beginning of February could see his weight change again in the coming months.
Just for the heck of it, how about the players who, between 2011 and 2012, added a significant amount of weight? The table is the same as the table above.
You could say there might be something there. All the same caveats apply, though. Itās UZR, the sample is even smaller, the players got a year older, and the whole sample might be thrown off by Franklin Gutierrez, who didnāt play that many innings in 2012. Gutierrez was also recovering from an illness, although he was more ill in 2011, when his defense was great. If you donāt trust the Gutierrez numbers, and you remove them, the average numbers balance out. If you leave them in, you get precisely this table. Itās included more for curiosity than for analysis. We need more data, and Iām thinking about collecting it.
Jhonny Peralta wants to get better in the field, so he lost a lot of weight. Thatās good ā itāll make him healthier, and it could improve his durability. But we donāt have much evidence to suggest heāll take a statistical step forward, and if you look at players who gain weight, the data also isnāt conclusive. We do need a lot more of it, however, so thatās something to keep in mind. As intuitive as it is that being in better shape could make your defense better, in reality weāre probably talking about very slight differences, if any differences at all. Whatās hugely critical for defense are instincts and first steps and hand-eye coordination and arm. Losing weight could make you a little quicker, but probably not significantly so, and in Peraltaās case, itās unlikely a matter of 18 pounds could make him more able to get to a bunch of grounders in the hole. Peraltaās range has only a little to do with his physical frame, or at least the parts of his physical frame he can change.
Itās good that Peraltaās in better shape. Maybe heāll keep that up all season. Maybe itāll have real, meaningful benefits. I just wouldnāt expect him to channel his inner Andrelton Simmons. What Jhonny Peralta was, Jhonny Peralta probably will be.