Fastballs and Change-Ups: Jimmy Rollins

Late to the party as usual, for the past few weeks I’ve become more and more interested in pitch-type linear weights for hitters.* In particular, I was curious as to what they might reveal about which hitters are particularly good at hitting particular kinds of pitches. For example, we sometimes call certain hitters “fastball hitters.” I’ve heard one of particular minor leaguer who shall remain nameless who hasn’t been called up because he allegedly has a “slider-speed bat” (given the dearth of other players in that particular organization that can hit the slider, you’d think that would be seen as a good thing…). And so on.

I thought that it would be interesting to look at differentials in linear weight values between pitches for different hitters. I found some interesting stuff, but I want to avoid the illusion than pretend that I’ve “discovered” anything at this point, so I’ll begin with a post (or two) about an individual . In the spirit of Dave C.’s earlier “questions” posts, this is the beginning of a conversation (and I hope to get more in-depth later) rather than the conclusion of a study. For today, I want to talk about Jimmy Rollins‘ recent problems against the fastball against the backdrop of his continued success against changeups.

* If you haven’t already read Dave Allen’s clear and excellent explanation of how pitch type linear weights work, I strongly recommend that you do so.

While Rollins is still a good player overall, there’s not denying that 2009 was a down year offensively, as he put up a mere .316 wOBA after a very good .357 in 2008 and an excellent .378 in his 2007 MVP campaign. This is well known. There could be different reasons for it (which may all have roots in age-based decline), for example, bad luck on balls in play. But what also stands out are his pitch-type linear weight values against fastballs and changeups.*

* Those of you who dutifully read Dave’s article already know that the linear weights are by count, there is the chance, of course, that recently Rollins is only falling behind on fastballs then crushing them later, but that seems pretty unlikely, and for simplicity we’ll be ignoring that possibility for now.

Over the last three seasons (2007-2009), Rollins has been +6.3 against fastballs, and +22.8 against changeups during the same period. As one might expect, during that time his best season against fastballs was 2007, when he was +10.7. He was even better in 2006, at +20.4. However, he’s been in (apparent) decline against fastballs since 2006 and 2007, sporting a -1.8 in 2008 and a -2.7 in 2009. His rates per 100 fastballs bear out the decline as well: from 0.58 in 2007 to -0.12 to -0.17.

In contrast, Rollins continues to be consistently good against change-ups. While prior to 2007, his numbers against changeups where generally unimpressive, in 2007 he smashed them for +13.3, and while he hasn’t been as good (against much of anything) since then, while he numbers against fastballs dropped off, in 2008 he was still +4.5 (+1.29/100) against changeups, and in 2009 +5.0 (+1.36/100). More interestingly, of the good hitters I looked at (bad hitters are terrible against most everything), Rollins had one of the biggest “gaps” in his numbers between fastballs and changeups. I’m curious as to what this means.

Obviously, players typically lose ability as they age, but I’m curious if the linear weights tell us something specific about how that works for hitters. I apologize for ending with questions, but that’s better than presumptuous answers. I want to know if readers a) have any insight (even educated guesses) into what’s going on with Rollins in particular and/or b) want to see more stuff on this. Is Rollins “sitting changeup” more often as he gets older? Maybe, I don’t know for sure from the data I have. It would be easy to say he’s doing this because he’s aware that he’s “lost bat speed,” but to me, that is also a leap — “bat speed” is a useful scouting term, but it is too quick to infer anything about that that from the data I’m looking at. Perhaps an aging study can be done down the road using this or other data. I don’t know what this means right now, but I’m interested to see if we can find out.

Matt Klaassen reads and writes obituaries in the Greater Toronto Area. If you can't get enough of him, follow him on Twitter.

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12 years ago

The first thing I would want to know is “how much regression to the mean do hitter pitch values deserve?” Rollins saw 376 change ups in 2009. But how many does he need to see before we say “Rollins ability to hit change ups is changing?” (For every baseball stat, the first thing I want to know about it is “What’s a small sample size for this stat?” The second thing I want to know is “How many runs is it worth?” We’ve pretty much got the second one nailed for this stat…)