The ranking might change day-by-day, Jarrod Parker said, but he agreed: “Overall I would say the fastball and changeup are my two better pitches.” And that changeup is special — he threw it more than any secondary pitch last year, it was his best-rated pitch, and a big part of why he had the 21st-best swinging strike rate among qualified starters. It wasn’t always that way, though. Coming out of high school, Parker was a fastball/curve guy. So what happened?
“I got hurt and didn’t want to throw as many breaking pitches, so I started working on a changeup.”
Maybe that doesn’t seem like a big deal to some, but I’ve been interested in this for a while. Some flawed research of mine once provided preliminary findings that high-slider pitchers like Brett Anderson were prone to injury, and then Jeff Zimmerman followed with a more statistically robust approach that backed up the general finding that the slider and curve are tough on the elbow. The fact that a Tommy John survivor was now telling me that he didn’t want to throw those pitches as much after his surgery — that fact actually physically caused me to lean in to his physical space a bit, and Parker gave me a look as he reached for his cleats.
Has the link between sliders and injury ever been made to him in an explicit manner? “Yeah — when you come back, there’s a reason why they limit you to so many [breaking balls] per batter, per inning,” Parker said. After asking him if his pitching coaches were familiar with the research that suggested sliders and curves were tough on elbows, he nodded, agreeing, but perhaps not willing to get into too much detail about his past and present relationships with different coaching staffs.
There was a little more. Parker talked about fastball control, and throwing quality strikes with both of his fastballs. He said that despite this current blip, he throws the same bullpen every time out — “about the same exact ratio of pitches I throw in my warmups” — and that he likes to keep things on a routine. I asked him about first strike percentage, something I’ve found to be well-correlated with walk rate, but he said “baseball is a game of adjustments” and that just the other day, the Tigers were doing a lot of first-pitch swinging. He didn’t necessarily feel like the first pitch strike was what was missing right now.
But I knew I already had something I wanted to check out when I got in front of a computer. Did pitchers coming back from Tommy John surgery use the slider less?
It’s a tough thing to really nail, since the PITCHf/x era only started in 2002 and your pool of Tommy John survivors with significant pre- and post- surgery PITCHf/x information is not large. The classifications themselves have changed slowly over the years, which might obscure real changes. And then there’s the simple fact that pitchers change and don’t change primarily based on performance issues. If you’re a reliever with a great slider, you may limit the sliders as you rehab, but when it’s time to get batters out in the bigs, you’re probably headed back to your best pitch to get the strikeout.
All of that said, it’s possible there’s some evidence that pitchers returning from Tommy John surgery use the slider less often.
The larger sample, which includes relievers and starters — 57 pitchers in all — shows a slight effect. Thanks to Brian Cartwright, who queried the PITCHf/x pitch types of this group in two classifications (a year before the surgery to two years after the surgery date), we can see that the slider is the only pitch that was used less often by the group when they came back from surgery:
|Average Difference, Post-Surgery||-0.004||0.051||0.017||0.010||0.086|
Already you can see a problem or two. The cutter usage leaps forward, so this could all be due to the change in classifications. Then again, since 2004, the overall slider percentage in baseball has stayed steady around 14-15%. In the end, the fact that 24 of the 47 pitchers that used sliders before and after surgery used the slider less is not a robust finding.
Limit it to starters, though, and it gets a little more interesting. And it does make sense to limit it to starters — starters have more pitches, by definition, and therefore can better diversify if one of the pitches causes them elbow stress. Since we’re down to 24 pitchers now, let’s just show the full sample:
|SL DIFF||FC DIFF||CU DIFF||CH DIFF||FS DIFF|
|Jorge de la Rosa||SP||-0.049||-0.059||0.151|
|Rubby de la Rosa||SP||-0.065||-0.010||-0.026|
Now the decrease in slider usage is more prominent. It could be erased by the increased cutter usage overall, but not once you look at it on a pitcher-by-pitcher basis. 14 of the 21 pitchers that used the slider before surgery used it less often after. If you discount any pitchers that showed opposite signs in their slider and cutter classifications, eight of 13 starting pitchers used the slider less after surgery.
The percentages aren’t huge. Parker lumped curveballs and sliders into one group, and we don’t see that sort of effect here for curves. But it does look like the conventional wisdom that Parker references — use the slider less during your Tommy John recovery in order to protect your elbow — underlines the sort of stress that snapping off a sharp slide piece can put on your ligaments.
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