CHICAGO – Zack Wheeler, Phillies catcher J.T. Realmuto said, attacks batters with the craftiness of a pitcher who relies more on stuff than velocity. He commands both sides of the plate, throws his fastball up and down, and has four pitches in his arsenal. Wheeler is a thumber.

A what?

“A thumber. People know that. It’s a baseball term,” Realmuto said Monday at Wrigley Field. “You don’t throw hard, but you command the baseball really well. Change speeds a lot. Move it around. Guys who don’t necessarily have the stuff to get outs, but they can do that because they command the baseball really well. He does it throwing 98 mph. It’s pretty fun.”

Wheeler’s average fastball this season, 97.1 mph, ranks in the top 2% of major league starters. But the 31-year-old has not relied simply on his velocity to become one of baseball’s premier starters. Wheeler, who finishes his first half on Wednesday night against the Cubs, has evolved over the last two seasons into a complete pitcher. He’s not just a power arm. He’s a thumber with a power arm.

“It’s so much fun to work with him because you can call a game like he’s a thumber,” Realmuto said. “Guys who can command the baseball throwing 88, 89 and do this and that. But he does that throwing 98. It’s really fun.”

Wheeler entered Tuesday with the major league lead in strikeouts (139) and innings (114) and an ERA (2.05) that is the third-best in the National League. He leads all players, not just pitchers, in WAR (5.3) and has allowed the third-fewest homers per nine innings in the National League.

He has a chance to start next Tuesday’s All-Star Game, which would make him the first Phillies pitcher to start the game since Roy Halladay in 2011.

Wheeler has found success this season with an improved cutter that complements his already effective four-seam fastball. Realmuto said Wheeler was reliant in the past on his two-seamer against left-handers, but he noticed they were sitting on it. So it helped to have another pitch to turn to. It helped to be a thumber. He started throwing his four-seamer, which has an increased whiff rate this season of 5%, against lefties, and then using that to set up his slider.

“He’s just evolving and coming into his own as a pitcher,” Realmuto said. “He understands how good he is, and he’s gaining a lot of confidence. The way he can locate both sides of the plate to both hitters, there’s not a lot of pitchers in the game who throw four pitches and actually command fastballs to both sides of the plate, up and down. It’s very rare that someone can do that, and he’s one of the guys who does it with a 98 mph fastball.”

Realmuto faced Wheeler 20 times before the pitcher signed last season with the Phillies. He had good numbers against him, 8-for-18 with two doubles, but that was before Wheeler seemed to move himself last summer into the group of baseball’s elite arms.

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In 2019, Wheeler threw fastballs for 59% of his pitches, which was the 10th-highest rate among all starters. He pitched with Noah Syndergaard and Jacob deGrom in a New York Mets rotation that relied on power as all three averaged more than nine strikeouts per nine innings.

Wheeler threw his fastball last summer just as often, but he no longer was chasing strikeouts. Instead, he induced weak contact and posted the third-highest ground-ball rate in the majors. He wasn’t just a power arm. He used his fastball to set up his sinker, changeup, and curveball, as all three of those pitches generated ground balls more than 50% of the time they were put in play.

The Phillies signed Wheeler for $118 million over five years largely because of his powerful fastball. But he pitched last summer with craftiness.

“I think the stuff is pretty similar,” Realmuto said when asked to compare the Wheeler he hit against and the Wheeler he now catches. “Execution-wise, he’s come a long way. Just being able to command both sides of the plate. ... I think just using his repertoire more, but the actual stuff itself is pretty similar.”

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DeGrom was the likely choice to start next week for the National League, but he said Sunday that he is leaning toward not traveling to Denver for the All-Star Game. Wheeler would have plenty of rest to pitch a few innings on Tuesday night against the American League and has a strong case to be deGrom’s replacement.

“If anybody is, it’s hard for him not to be the guy. Right? I think with the way he pitched last year, and he’s taken another step this year,” Realmuto said. “Obviously, Jacob deGrom is the best pitcher on the planet, and that’s not exactly debatable. But if anybody is in that next class or in the class with him, I put Zack up there with anybody.”