Is the Phillies’ dominant starting pitching sustainable all season? Their catcher thinks so.

J.T. Realmuto sat down Wednesday morning at Angel Stadium, powered up his iPad, and jotted notes on a scouting report. He does this before every game. It’s part of the Phillies’ process of formulating a game plan and delivering it to the starting pitcher.

Lately, though, Realmuto is enjoying his homework as much as ever.

The Phillies are off to their best start — 21-11, including 13 wins in the last 16 games — since 2011, when they set a franchise record with 102 victories. The surge has been built largely on the backs of the starters, whose collective 2.50 ERA is the lowest among National League rotations and second in the majors to the Boston Red Sox (2.03).

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And like every positive early-season trend, it comes with a question: Is this sustainable?

History says probably not. Since 2012, five teams have finished a season with a sub-3.00 ERA from their starting rotation, none better than the 2022 Dodgers’ 2.75 mark. Last year, the San Diego Padres’ rotation led the majors with a 3.69 ERA. In 2011, the Phillies’ “Four Aces” rotation of Roy Halladay, Cliff Lee, Roy Oswalt, and Cole Hamels came in at 2.86.

So, yes, there’s bound to be slippage. But Realmuto is here to say that there’s staying power in what Zack Wheeler, Aaron Nola, Ranger Suárez, and the other Phillies starters are doing.

“They all have so many weapons that are so good that you can really pitch,” Realmuto said this week in Anaheim. “I know it’s an older term, but literally, it’s pitching. It’s the art of pitching as it was meant to be.”

Indeed, at a time when most teams are prioritizing velocity, the Phillies’ rotation is a throwback. Through Wednesday, Phillies starters were tied for 27th in the majors in average four-seam fastball velocity at 92.7 mph. The MLB average was 93.7 mph. Only Wheeler (94.5 mph) is above that bar.

As a group, the Phillies’ starters also throw fewer fastballs than their peers. Through Wednesday, they ranked 24th in four-seam usage (15.7%), well below the league average (18.5%).

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“We have guys who have great stuff, but they all have the ability to do multiple things and mess with hitters, mess with their timing, do something different from at-bat to at-bat,” Realmuto said. “From game to game, they’ll attack hitters differently. The ability to do that makes my job a lot of fun. Because it’s not just, ‘here’s a fastball, here’s a slider.’”

If anything, it’s the Phillies’ use of the two-seamer, or sinker, that might set the rotation apart. They were tied with the New York Mets for the highest two-seam usage (17%), with Suárez and fellow lefty Cristopher Sánchez known for getting weak contact with bowling-ball sinkers.

It’s possible the Phillies are simply ahead of the curve. Given the recent emphasis on launch angle and hitting balls in the air more frequently, pitchers focused on elevating four-seam fastballs above the barrel for strikeouts. But as hitters have adjusted, pitchers who can get weak contact on the ground are thriving.

Take Suárez, for example. In leading with his two-seamer but also developing a curveball that he barely threw two seasons ago, he has the third-highest ground-ball rate (60.8%) among 133 pitchers who have tossed at least 20 innings this season. He’s also tied for the third-lowest exit velocity (81.9 mph).

“You see more guys today that can hit fastballs at the top of the zone than you did three years ago because [high fastballs] got so popular,” Realmuto said. “Now the pitchers are making the adjustment again, being able to throw sinkers and get under barrels. That’s the thing with our guys. They can all do both.

“If a guy’s a really good four-seam hitter, we won’t show him the four-seam that day. We’ll just attack him with sinkers. Or if a guy’s a good sinker [hitter], do the opposite. The ability to do both just kind of changes the game.”

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It’s one of the things that makes Wheeler elite. He can run his four-seamer up to the mid-90s but also sink his two-seamer to righties. He developed a splitter in spring training to help against lefties, and it’s working. Lefties have hit .213/.294/.387 against him so far, compared to .261/.310/.412 last season.

And then there’s Nola, who ranks in only the 10th percentile in average fastball velocity (90.9) but throws two fastballs in addition to his signature curveball and a changeup and cutter.

“Stuff comes in different shapes and forms than just velo,” pitching coach Caleb Cotham said. “There’s ways to promote uniqueness rather than just raw output that is definitely part of our conversation. Velo’s not the only lever you have to pull.”

And as a catcher, Realmuto has no shortage of buttons to push on his PitchCom device when he’s calling a game for the Phillies’ starters. It helps to have options when one pitch isn’t working particularly well or a particular lineup is better suited to hit one pitch than another.

It’s also why Realmuto believes the Phillies’ rotation isn’t due for much regression from a stellar April.

“For me, the track record’s there, really,” Realmuto said. “I don’t think there’s any reason to believe they shouldn’t keep it up. Obviously it’s hard to keep up the pace they’re on now. But I think they’re the best rotation in baseball. If they’re healthy and they’re feeling good, they’re all so talented that there’s no reason they can’t keep it up for the entire season.”