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.

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

12 Responses to “Fastballs and Change-Ups: Jimmy Rollins”

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  1. philosofool says:

    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…)

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  2. yankee82093 says:

    Batspeed is not something only scouts use. Hittracker online has batspeed for homeruns hit. Using this tool, we can see that his batspeed has declined from 103.4 in 2007 to 101.5 in 2008 to 100.9 in 2009.

    It would be interesting to see the correlation between batspeed and the ability to hit a baseball. This could probably be done pretty crudely now with hittrackeronline, but you could something pretty accurate once hit/fx becomes available, if it ever does.

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    • Good points. I should have written more what I mean: it seems to me that what scouts mean by “bat speed” and literal “speed of the bat” are two different things.

      I’m not sure we’re talking about the same thing, though — I thought hit tracker just tracked (or publishes) the speed of home run balls off each player’s bat, not his bat speed. Maybe I’m looking in the wrong place?

      Hit f/x will be sweet.

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      • yankee82093 says:

        You’re right about that on hittrackeronline. It does measure speed off bat, not bat speed.

        However, if we make the assumption that he hasn’t changed the weight of the bat he uses (maybe a big assumption, idk), and the assumption that the average speed of all the pitches that he has seen across that interval is the same in each year, then wouldn’t there be a direct relationship between speed off bat and batspeed?

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      • don says:

        I think it’s only speed off bat for his hits that happened to be home runs. It probably tells you some general things (i.e. Mark Reynolds can hit the ball harder than almost anyone else) but I’m not sure it’s that useful for a 2% change for a guy who’s hit 62 home runs over his last 2100 PAs.

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  3. yankee82093 says:

    meant fastball, not baseball.

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  4. The A Team says:

    I’m going to guess that the prospect with the slider speed swing is Kila Ka’aihue.

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  5. Peter Jensen says:

    However, if we make the assumption that he hasn’t changed the weight of the bat he uses (maybe a big assumption, idk), and the assumption that the average speed of all the pitches that he has seen across that interval is the same in each year, then wouldn’t there be a direct relationship between speed off bat and batspeed?

    The answer to this question is no, there is no direct relationship between bat speed and speed off the bat. Speed off the bat is dependent on a number of factors of which bat speed is one. Where on the bat the ball is hit is another important factor. Actually it is two important factors because where it is hit along the length of the bat is important and so is where it is the offset between the balls center line of its direction of travel and the bats center of its swing arc. Plus, Rollins is only hitting 20 to 30 home runs a year so there will be significant variation just due to small sample size.

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  6. Peter Jensen says:

    Matt – I am glad to see you using pitch f/x to analyze hitters strengths and weaknesses. This is an area that I thought had much potential and had not been the focus of much attention until recently. You also recognized one of the potential problems with your pitch type analysis, that different pitches are used in different counts and that the batter does not have the same incentive to swing in every count. You may want to see whether limiting your analysis to just the pitches where a batter swings yields a different interpretation of where his strengths and weaknesses are.

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    • Heh… yeah… that’s the thing. That _would_ be the way to do it, but I’d have to get my own Pitch F/X database first. It will happen eventually, but at the moment I don’t have one. Some of the new heat-maps out there are very cool

      It’s fun to see how far I can get with just pitch-type lwts for now with the BIS classifications, but you’re right that it needs to be taken further. This (and some other) posts are just “post its” for future research.

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