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What Statcast tells us about catchers and stolen bases
- Updated: December 14, 2016
On May 9 in Cincinnati, we saw what may have been the least likely caught stealing of the season. In the eighth inning of a game the Pirates would go on to lose, 3-2, Pittsburgh catcher Francisco Cervelli accomplished the near-unthinkable: He nailed Billy Hamilton trying to steal second base.
We say that because Hamilton is regarded as baseball’s pre-eminent basestealer and because Cervelli has been victimized more than any other recent catcher. Since the start of 2015, Hamilton has swiped 115 bags in 131 attempts, making for an outstanding 87.8 percent success rate that’s the highest in baseball among the 77 runners with 30 steal attempts in that span. Meanwhile, no catcher has allowed more stolen bases over the same time than Cervelli’s 168 — all the more remarkable because he wasn’t even on the field for large chunks of time in 2016 due to a variety of injuries.
On paper, it was just about as big of a mismatch as you can get. Dancing off of first base with a 1-1 count to Joey Votto, Hamilton took off. The pitch, measured by Statcast™ as an 87.1 mph slider from Ryan Vogelsong, was slightly inside, and the throw from Cervelli to shortstop Jordy Mercer was on target.
“Got him! What a throw by Cervelli… wow!” exclaimed the Cincinnati broadcasters, certainly unaccustomed to seeing Hamilton get thrown out.
The throw’s velocity was measured as being 79.2 mph. Is that why he caught Hamilton? Is that even good?
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To answer the second question, we need to be able to look at large samples of catcher throws from across the Major Leagues in order to have data to compare Cervelli’s throw to, and we’d never been able to do that prior to 2015, when Statcast™ came online.
Before that, we oversimplified. We judged the qualify of catchers based largely on caught-stealing percentage, even though we know that in reality the path to “safe” or “out” on each attempt is really an intersection between a variety of events controlled in part by the pitcher, catcher, runner and even the infielder.
Let’s focus on just one of those skill sets: arm strength. Using Statcast™ data, we looked at 1,701 tracked catcher throws to second base on steal attempts from the 2016 season, which broke down into 1,151 successful steals and 550 outs.
The number of tracked throws isn’t close to being equal to the total number of steal attempts of second base, but it’s not expected to be, either, because not every steal attempt draws a throw. Think of how many times a catcher doesn’t catch a ball cleanly and doesn’t bother with a throw, or throws to third rather than second on a double steal.
It’s more than enough data for a reasonable sample size, so we’ll use it and start with a simple question: Is there a relationship between average arm strength and caught-stealing percentage? Yes. Sort of.
What you see here are the 59 catchers with 10 or more tracked throws to second on steal attempts in 2016, and there’s unquestionably some relationship there, though there’s a pretty wide distribution around that trendline, too.
Points in favor of “yes, it matters” would be that the lowest caught-stealing percentage belongs to Tyler Flowers, who has a weak arm, while one of the highest is Gary Sanchez and his strong arm. Points in opposition would include the fact that Russell Martin and Salvador Perez had similar arm strengths (80.9 mph for Martin, 81.2 mph for Perez), yet had wildly differing success rate (15 percent for Martin, 48 percent for Perez).
At the very least, we can say that it’s hard to be very good with a poor arm, and that you’re unlikely to be terrible with a strong arm, but there’s still a lot …
