J.T. Realmuto has a reputation as one of baseball's most athletic catchers, and perhaps that's because he hasn't always been a catcher. When Realmuto was drafted by the Marlins in 2010, he was listed as a shortstop, where he'd played on a state championship team in high school. He also had opportunities to play quarterback at Division I football factories; instead, he chose baseball, and now he's developed into one of the better young starting backstops in the Majors.
It's one thing to say that Realmuto looks athletic, of course, and another thing to actually quantify it. But as we continue to progress with using Statcast™ metrics to help improve our understanding of catchers, we're continually learning one thing: Realmuto constantly stands out.
Take foot speed, for example. Our latest public metric is called "Sprint Speed," and it measures how many feet per second a player covers in his fastest one-second window. The slowest runners average about 23 ft/sec and the fastest hit 30 ft/sec, making the Major League average 27 ft/sec. Realmuto, at 28.7 ft/sec, easily tops every other catcher. He tops shortstops like Corey Seager and Zack Cozart. He tops center fielders like Jonathan Jay and Joc Pederson. He's a catcher.

Realmuto recently talked to MLB.com about how his multi-sport background helped him.
 "I've always been fast, from playing football, basketball," said the Miami catcher. "It didn't matter, whatever sport I was playing, I was always running. I tried to do my best to keep my athleticism with where it's at.
"Even when I wrestled back in the day, my footwork, I feel like all that has contributed to my speed. I have other athletes in my family who were fast too. It has a lot to do with genetics, but I think, growing up in those sports, and being around it all the time, it's helped."

It sure has. Since 2015, Realmuto's 23 stolen bases are the most of any catcher, and that's a decent proxy for foot speed, but we've always known we can do better than that. Steals are based in part on opportunity, reactions, and the willingness of management to give the green light. What we're interested in here is the actual skill of speed, and Realmuto isn't merely baseball's fastest catcher. Other than Dee Gordon, who is one of the half-dozen fastest players in the game, there's no other regular Marlin faster than Realmuto, who is essentially tied with outfielder Christian Yelich (28.6 ft/sec). 
Realmuto was also the fastest catcher in 2015 and tied for fastest in 2016, so this isn't a one-year thing. It's impressive enough when you compare him to other positions, but it really does take on an entirely different dimension when you compare him only to his fellow backstops. Looking just at catchers, the average drops from 27 ft/sec to only 25.9 ft/sec, making Realmuto nearly three feet per second faster than others at his position. If that doesn't sound like much, think about what that adds up to over six or eight seconds running the bases. It's a big deal.
Baserunning Sprint Speed leaders (ft/sec), Catchers, 2017
28.7 feet per second -- Realmuto, Marlins
27.5 -- Willson Contreras, Cubs
27.3 -- Austin Barnes, Dodgers
27.1 -- Andrew Knapp, Phillies
27.0 -- Travis d'Arnaud, Mets / James McCann, Tigers
Realmuto is so fast, in fact, that it actually takes opponents by surprise when he beats out hits.
"I get it from infielders all the time," he said. "If I beat out a ground ball at the shortstop, every now and then, playing a new team, they'll take their time in throwing me out. They'll either just get me or sometimes I'll beat it. I'd catch them by surprise. The next time, they'd come into the box, they're like, 'Man, you are fast for a catcher. I didn't know you were that fast.' So it's still catching guys by surprise, guys I haven't played before."

Realmuto's athleticism manifests itself in other ways, too. While he's never been a strong framer, he's got truly elite pop time -- that is, he gets the ball out of his glove and to the infielder faster than just about any other catcher. Last year, of 57 catchers who had at least 10 steal attempts of second against them, Realmuto's average pop time of 1.89 seconds was the best in baseball, where the MLB average was 2.02 seconds. This year, his 1.91 second time is second only to San Diego's Austin Hedges, at 1.88 seconds.
When he nailed Philadelphia's Odubel Herrera trying to steal on April 27, he did so with a 1.38 second pop time that was the fastest ever tracked by Statcast™ on a steal attempt of second or third.

Remember when we said that the Major League average Sprint Speed was 27 feet per second? Herrera was flying down the basepath at a scorching 29.8 feet per second, but thanks to Realmuto (and pitcher Edinson Volquez), he still couldn't quite make it safely.
But if you look back to our top five fastest catchers list, you'll notice something. They're all young, with the 28-year-old d'Arnaud the elder statesman of the bunch. We talked about Realmuto playing shortstop in high school, and Barnes (second base, third base) and Contreras (left field) have each seen time at non-catching positions in their brief careers. Realmuto seems aware of how important youth can be behind the plate.
"Obviously, with catching, I'm going to slow down over time," said Realmuto. "I'm going to be less and less athletic the longer I catch. But my offseason is geared towards trying to stay as athletic as I can. In the weight room, I'm not trying to put on too much weight. I'm not trying to get too bulky. I'm trying to keep as athletic-fit as I can."
It's true. This won't last forever, because it can't. The demands of the position simply don't allow it to happen long-term. But for now, and for the last few years, the Marlins have a catcher unlike any other, one who has hit .298/.344/.438 (eight points better than league average) over the last two seasons, and one who may be deserving of a spot in the upcoming All-Star Game in Miami. He's not baseball's best catcher, not when Buster Posey is around. But he's almost certainly the most athletic, and the numbers back it up.