"It's extremely important," Realmuto said. "That's a huge part of the game -- stealing a strike here and there is something that really changes ballgames. Changing counts, the difference between a 1-0 and 0-1 count is huge to a hitter."
Realmuto, a converted shortstop, is still learning the ropes of catching.
Last year he was expected to spend the season at Triple-A New Orleans, but he was called up and named the everyday starter in April after Jarrod Saltalamacchia struggled and was designated for assignment.
Without that full season of Triple-A to further develop, Realmuto was learning on the fly in the big leagues.
"Last year, I worked a lot on blocking and throwing and all that," he said. "We need to kind of get back to the basics this year and kind of focus on [receiving]."
Advanced metrics show how a catcher receives pitches matters. According to Baseball Prospectus, Realmuto rated near the bottom in framing, costing Miami nearly 15 runs. Only Philadelphia's Carlos Ruiz rated lower.
"Basically, for me, it comes down to setup," Realmuto said. "How I set up, getting myself in a good position to be able to catch pitches in any part of the zone at any time."
Realmuto is watching video of other catchers, paying particularly close attention to Milwaukee's Jonathan Lucroy.
"He gives probably the lowest target in baseball, and he's one of the best receivers," the Miami catcher said. "That's something I'm going to work on as well."
Realmuto has the athleticism to improve. He's also among the quickest catchers in the game, and he showed it in his ability to pop out of the stance and throw to bases. Statcast™ tracked 1,784 pop times in 2015, and Realmuto had the best average time of the group. His average pop time was 1.867 seconds. The league average is 1.975 seconds.
"Just like everybody else, he's trying to get better," manager Don Mattingly said. "I know the metrics a little bit on that.
"J.T. is a terrific athlete -- a guy that works hard. Has a good attitude. We're going to work. We're going to try to continue to get better in all areas. That's with every player."
Non-roster invitee Troy Patton, a 30-year-old lefty reliever, was released due to injury concerns. The Marlins now have 63 players in camp.