When it comes to pitching injuries, none is easier to relate to than the blister. Almost everyone has had one, which is more than can be written about a torn elbow ligament or a frayed labrum. Yet the accessibility and commonness of the blister hasn't led to a sea of information; pertinent details—like why certain pitchers seem predisposed to suffering from repeat cases, and how those pitchers can be identified ahead of time—remain unknown.
Perhaps it's because the treasure isn't worth the hunt. If a pitcher shreds his elbow, he'll miss a season; if a the tip of a pitcher's finger bubbles, he might miss a start—in 2013, Miguel Gonzalez was the lone big-league pitcher to spend time on the disabled list due to one. It's no surprise then that the average article about blisters focuses on the myriad (and often zany!) ways pitchers treat them. Take the Wall Street Journal's detailed breakdown of C.J. Wilson, the league's leader in blisters since 2009, for example:
"In addition to shaving the blister, Wilson coats it in superglue, smears ointment on it, soaks it in iodine and a low-pH solution to prevent infections, and runs a LiteCure laser over the area to promote skin growth. As a teenager, he said, he once ripped off his entire fingerprint, and he has to be careful even now not to worsen the blister whenever he tends to it."
It sounds like he's tried everything. He's soaked his hands in clubhouse staples like pickle brine. He's thought about changing the way he grips the ball. He tried wearing a sock on his throwing hand when he long-tossed between starts. He's consulted with burn doctors in Miami on ways to strengthen his skin. For a time last year he had success with something called Stan's Rodeo Cream, a gooey brown ointment invented by Dodgers trainer and former rodeo cowboy Stan Johnston.
However enlightening (and disgusting) those pieces are, they leave us without an important part of the story: Why, exactly, those pitchers are victims of spotty skin.
Answering complicated questions requires starting with the basics. Beyond the obvious real-word causes of blisters—chemical burns, exposure to extreme temperatures, and the like—there's a special subset revolving around repetitive activity, be it gripping a bit or throwing a ball. "The main type [of blister] that we are talking about in pitchers are caused by friction," our resident injury expert Corey Dawkins wrote in an email, "which are caused by irritation between the superficial layers of the skin and the deeper layers."
Friction is a friend and an enemy to pitchers. Changing finger position and pressure allows pitchers to manipulate the ball's direction and speed, yet the constant interaction between the finger, seams, and fingernails set the stage for blisters. Add in some heat after a winter of inactivity—"Pitchers have to take some time off from throwing in the offseason to allow everything else to heal so it's inevitable that the skin will lose the toughness factor in the offseason," Dawkins explained—and springtime blisters are almost a foregone conclusion. Teams can tolerate a blister during the exhibition season, but when they carry to the regular season it becomes a problem.
So why do certain pitchers have this issue? Conventional wisdom suggests it could do with pitch usage: the more seam-intensive offerings a pitcher throws, the more exposed he is to developing a blister. Different pitchers have different grips, but two-seamers and sliders are speculated as culprits more often than others. Could the answer really be as simple as what pitches they throw? Probably not. Before delving into the methodology and results, let's address two potential problems here: 1) an incomplete data set—it stands to reason not every blister gets reported; and 2) potential survivor bias—we're only using big-league pitchers here due to the potential shakiness of minor-league injury data.
Using that data, Russell Carleton ran a logistic regression for every big-league pitcher with a 50-plus inning season from 2009-2013. He used the pitcher's total pitches thrown, their blister history, and rate of two-seamers and sliders thrown as predictors. The worst predictor, it turns out, was the rate of seam-intensive pitches thrown, as it checked in with a .214 p-value. (For the uninitiated: lower p-values are more suggestive.) The best predictors, both of which qualified as statistically significant, were raw pitch count and whether a pitcher had suffered a blister in the previous season (each had a p-value of .003).
Changing the parameters from the rate of seam-intensive pitches to the total doesn't change things too much, either. That p-value improves to .130, but previous blisters (.004) and pitch count (.072) remain more significant. The story remained the same when a 100-inning floor was imposed, and when other pitches were tested on an individual basis. As Carleton said, "If there's a lesson here, it's that throwing a lot of pitches leads to blisters, as well as previously having a blister problem. The type of pitches that you throw isn't as powerful a predictor as is a heavy workload."
It's not a sexy answer but it makes sense on two levels: for one, the more pitches a pitcher throws, the higher the chances of any injury, including a blister; for another, if we had two people who were the same across the board except only one had been bit by a dog before, and we were asked who was more likely to be bit by a dog heading forward, we'd choose the past victim. Why? Because we can infer that person interacts with dogs in some way or another. Same thing here. A pitcher who suffers from a blister probably has the characteristics—be it long nails, sensitive skin, humid home park, and pitch mix—in place, which could lead him to develop another one.
Baseball's most controversial blister developed during Game Six of the 1986 World Series. Roger Clemens had the Red Sox in position to win the championship, having thrown seven strong innings, when a blister on his finger proved to be too much. Fearing his effectiveness would wane, the Rocket told manager John McNamara he was done for the day. McNamara had no choice but to insert the bullpen, which blew the game with help from Bill Buckner. A Game Seven defeat later, the trio of Clemens-McNamara-Buckner would become the latest goats in Red Sox' lore.
Accounts of the Clemens-McNamara exchange have changed over the years, with parties offering varying (and possibly apocryphal) stories. Although two of Clemens's teammates defended his honor in Jeff Pearlman's The Rocket That Fell to Earth, McNamara contested their account in a MLB Network special. The former manager not only maintained Clemens had asked out, but downplayed the injury—calling it a skin tear—and questioned the blister story's origin. Perhaps the last part was a jab at Clemens, who told reporters after the game, ''My blister was at a point where I couldn't finish off my slider."
Clemens's misfortune makes for an interesting case study, as he has the two things that qualify as the best blister predictors: a large workload and a past encounter. While exact pitch count data isn't available for 1986, Clemens threw a career-high 254 regular-season innings and added 33 more in the postseason—a sizable total for a pitcher who previously hadn't topped 200 innings in a professional season. Clemens didn't deal with a blister in 1985; however, he did leave a start five weeks before Game Six due to one on his thumb. Did Clemens suffer a blister during Game Six? No one can say for sure. But, if he did, it wouldn't be a surprise.
Special thanks to Russell Carleton, Corey Dawkins, and Harry Pavlidis.