Bartolo Colon, Surgery, and Sample Size

Some interesting news came out this week regarding Bartolo Colon and his path back to the Major Leagues. Last spring he had stem cells surgically inserted into his elbow and shoulder, and this somewhat experimental procedure is now receiving a lot of notoriety due to Colon’s surprising success so far this season. I’m not a doctor and realize that I have limited insight into medical procedures, so I’ll stay out of the debate about how effective this surgery may or may not be, but I do think that we need to keep in mind the reality of Colon’s performance when talking about whether this kind of procedure will be “the future of sports medicine”.

There’s no doubt that Colon has generated terrific results for the Yankees so far this year; his 2.81 xFIP is the lowest of any pitcher in the American League. He’s pounding his fastball for strikes and hitters are having problems doing anything with it. But if you look beyond just the raw results, there are some markers that indicate that this version of Colon isn’t all that different from prior versions.

Let’s start with his strikeout rate, which has been the lynchpin to his success so far. His 8.92 K/9 is way above his established career norms, and would represent his best mark since 2001. His swinging strike rate, however, is just 5.7%, lower than it was any of the last three seasons he took the hill. The only AL pitchers who are getting fewer swings and misses than Colon are Brad Penny, Ivan Nova, Tyler Chatwood, Wade Davis, Doug Fister, and Nick Blackburn. As a group, those guys have a collective K/9 of about 4.25, less than half of what Colon’s strikeout rate is.

As has been noted around the blogosphere, swinging strike rate has an extremely high correlation with strikeout rate (for obvious reasons), and is actually a better predictor of future K/9 than past K/9 is. Colon’s swinging strike rate is so low that it’s going to be nearly impossible for him to maintain this kind of strikeout rate going forward.

Whether he’s just been the beneficiary of some friendly strike zones or batters are so surprised that he’s throwing strikes that they forgot to swing does not really matter all that much – we have to expect that Colon won’t keep freezing hitters at the rate he has been, and his strikeout rate will probably return to something closer to his previously established norms.

Now, I know that it seems natural to think that Colon’s jump in called strikes could be due to this huge velocity spike he’s gotten since undergoing the surgery, but there’s only one problem – he hasn’t actually gotten a huge velocity spike. Despite all the talks about a “95 MPH fastball”, Colon’s average fastball speed this year is 91.7 MPH, essentially the same as it was in 2008 with the Red Sox. Sure, he’s hit 95 from time to time this year, but he’s always done that; his normal velocity is in the low-90s, though, just as it has been for most of his career.

His velocity is up from where it was in 2009, but that was a sample of less than 1,000 pitches and he was battling arm problems at the time. It’s not that surprising that a pitcher who had any kind of surgery after losing some velocity would get it back once he had recovered from his ailments, and that’s essentially what we see with Colon. He’s not throwing harder than he used to – he’s just back to what he was before.

And perhaps that’s the key point here. The miracle surgery narrative is being helped along by this perception that Colon was this awful, useless pitcher who couldn’t get Major League hitters out anymore, but that’s not what the data shows. He had one bad half-season in 2007 where his BABIP spiked to .357 and he posted a miserable 6.34 ERA, but his peripherals were good and he predictably rebounded to be a useful pitcher in both 2008 and 2009. Colon has never been lousy. This surgery didn’t make a bum into an ace because he was never a bum to begin with.

That doesn’t mean the surgeon is a fraud or that this technique won’t prove valuable in the long run. For one thing, Colon hasn’t broken down yet, so that’s new and different from previous years. If he manages to stay healthy all season, I’d imagine this won’t be the last time this surgery is performed, and we’ll eventually get a better idea of just how effective putting stem cells into a pitcher’s elbow can be. We just need to avoid getting caught up in the story of how this surgery has turned Colon into a frontline pitcher, because there’s a lot of evidence to say that, at the end of the day, he’s not that much different now than he was a few years ago.

Dave is the Managing Editor of FanGraphs.

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13 years ago

In the lead doctors own words of talks with Colon “He could not throw the ball without horrible pain”. Now he’s back routinely throwing upwards of 92 mph and not complaining of any pain. That is pretty amazing. I agree that this year’s durability will have a lot to with looking at this surgery further, I don’t think k/9 or swinging strike or anything should though. How well he pitches shouldn’t really matter, how hard he is throwing and how long he can do it for are really what should be monitored at this point.

I am skeptical though of how much of the success of Colon coming back was due to the stem cell injection. Having worked in a stem cell research lab my knowledge of stem cells might be what some would call slightly above average. I realize stem cell’s growth and transformation into final tissues are greatly influenced by the tissues around them (secretions from those tissues actually) but this still seems a little like throwing paint at a canvas and hoping for art. I do think a more regimented rehab/training program could have played a significant role and nobody seems to talk about it. Much like Tommy John some pitchers see their velocity increase because they are simply in better pitching shape (arm strength, core strength, etc) than they ever were before. Bartolo has never been the pinnacle of fitness so looking after his arm and body better as part of this rehab may have had a significant effect and I feel it is being overlooked.

13 years ago
Reply to  Dave

Tendons/ligaments don’t really regrow… and certainly don’t repair themselves… unless you throw stem cells at them.

I wouldn’t say it’s like throwing paint at a wall and expecting art, more like filling a leaky bucket with rubber cement.

13 years ago
Reply to  descender

Say what? Tendons/ligaments do not repair themselves?? So no one ever recovers from a sprained ankle?

Antonio Bananas
12 years ago
Reply to  Dave

Funny you should say that. When you sprain your ankle, your tendons are nearly permanently stretched out. Yes they do heal, however the likelihood of reinjury is greater because the joint isn’t as “tight”. Tendons heal, just not perfectly.