Let me start by recommending that you all read the articles over at Fangraphs by Jeff Zimmerman upon which these are based (Here’s the link to one, that will link you to the rest). Zimmerman has done the dirty work of estimating injury probability for starting pitchers using a logistic regression (where your prediction is, in fact, a percentage probability) based on the primary universal factors that he considers important: pitcher age, starts made over the last 3 years and trips to the DL. The guys most likely to hit the DL will be older pitchers who have made fewer starts and taken more trips to the DL. Though the latter two are obviously closely related, a lot of what is being picked up is time shuffling between bullpen and rotation, minors and big league and the fact that young guys without a big league track record are more likely to go on the DL than young guys that have one. So… the guys least likely to hit the DL will be young pitchers who have made a lot of starts already without spending time on the DL.
It should come as no surprise that among the starters that Zimmerman has pegged to be the least likely to hit the DL is Rick Porcello (28.8%), a guy who is young and has made a lot of starts over the past three years without spending any time on the DL. Justin Verlander, Anibal Sanchez and Max Scherzer are a bit older than Porcello, but since both have also made a lot of starts without going to the DL they also come in with low injury risks (32.6% for Scherzer, 33.3% for Verlander and 33.7% for Sanchez). League average is 39%, so those are good numbers – even though they seem high. The fact that they seem high should serve as another reminder that rotation depth is always important. Doug Fister has spent time on the DL, so he comes in significantly higher than Scherzer and Verlander (44%) – previous trips to the DL are by far the most important predictor of future trips to the DL, relative to age and starts made. Drew Smyly didn’t make his list, since he didn’t throw enough innings in 2012, but his injury risk will be pegged higher than anyone but potentially Fister since (although he is young) he hasn’t made very many major league starts and has already hit the DL once.
Smyly’s injury was a severe blister and since we sort of have a tendency to see injuries followed by like injuries that has to be better than an elbow problem or muscle pulls/strains like Fister had. There is another reason for concern regarding Smyly though – in further research Zimmerman found that being among the top in terms of percentage of sliders thrown or percentage of curveballs thrown raises injury risk by 7 percentage points and 12 percentage points respectively. Smyly comes in barely under the threshold for being “among the top”, he threw sliders 29% of the time while Zimmerman set the threshold at 30%. A few Tiger relievers are well above that threshold though, Darin Downs (32.9%), Phil Coke (37.1%) and Al Alburquerque (62.3%). The only Tiger relievers to throw “too many” curves were Thad Weber, Collin Balester and (especially) Dan Schlereth (55.2% curves). Since Alburquerque and Schlereth did spend a lot of time on the DL last year – Zimmerman’s results get some instant credibility. I’d note that while Brayan Villarreal is a fastball-slider guy just like Alburquerque he is a FASTBALL-slider guy while Alburquerque is a fastball-SLIDER guy. Given the fact that Villarreal seems to go on the DL every season and every offseason, he obviously still looks like a big risk to do so again however many sliders he throws.
Those “offspeed percentages” aren’t factored into Zimmerman’s baseline projections, but none of the Tigers starters exceed them. They throw – mostly – hard and mix pitches up a lot. On those counts – they look like very good injury risks, Smyly aside. Zimmerman also found that starters that – by a variety of measures – tend to be wild also get hurt more often. He chalks this up to smooth mechanics or spurious correlation, since some guys hit the DL when nothing is physically wrong just because they can’t find the zone (like Dontrelle Willis). I’d add another channel: it’s harder on a pitcher’s arm to throw a lot of pitches in one inning than spread out over several innings. Tigers starters all pass on these criteria as well: they hit the zone a lot and don’t walk all that many guys. However, once again Al Alburquerque and Brayan Villarreal get a red flag here – at least for the most important measures, an unintentional walk rate over 10% (which gives a 10 percentage point increase in injury risk). On a second measure – percentage of pitches in the zone – you could add Joaquin Benoit: he was barely over the 47% threshold last year, but below it in 2010 and 2011. He doesn’t necessarily walk a huge number of guys, but he’ll go deeper into counts.
All in all, if the Tigers go with Rick Porcello as their fifth starter you’d have to say that the Tigers have either THE least injury-prone or one of the least injury-prone rotations in baseball. And that’s obviously a good thing, in a world where fill-in starters have ERAs of 9.00. If only we could say the same for our ‘pen.