Jacob deGrom throws one of the nastiest four-seam fastballs in baseball. It gets on hitters quick, sits between 95 and 96 mph this season and sometimes touches 97 or 98. It travels downhill from his lanky 6-4 frame, fooling batters into taking strikes in the bottom half of the zone and swinging through them in the top half. His arm is as live as they come — he wasn’t converted to a pitcher from a college shortstop so that he could float off-speed stuff all game.

That’s why when deGrom struggled out of the gate this season, it was somewhat confounding to see his four-seamer getting pounded by opposing players.

Hitters batted .215 against deGrom’s fastball through the first 54 games of this season, according to Brooks Baseball, a website that records PITCHf/x tracking data. That’s not catastrophic, but righties knocked his fastball to the tune of .228 in that same time span, a number higher than you want to see out of your one remaining ace.

Those struggles led to a 3.97 ERA and a 1.37 WHIP — much closer to the league-average marks of a 4.36 ERA and a 1.34 WHIP than the top of the rotation guys that deGrom is considered among. (Clayton Kershaw, among the best pitchers in baseball, has put up a 2.04 ERA and a 0.884 WHIP.)

If you section off deGrom’s four seasons into thirds, those are the highest marks for those two stats to date (excluding the final third of 2016, which was shortened due to ulnar nerve issues in his throwing elbow).

2014

Games 1-54: 4 starts, 2.42 ERA, 1.08 WHIP

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Games 55-108: 11 starts, 2.95 ERA, 1.34 WHIP

Games 109-162: 7 starts, 2.53 ERA, 0.94 WHIP

2015

Games 1-54: 11 starts, 2.41 ERA, 0.99 WHIP

Games 55-108: 9 starts, 1.73 ERA, 0.79 WHIP

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Games 109-162: 10 starts, 3.59 ERA, 1.18 WHIP

2016

Games 1-54: 9 starts, 2.62 ERA, 1.16 WHIP

Games 55-108: 10 starts, 2.23 ERA, 0.97 WHIP

Games 109-162: 5 starts, 5.72 ERA, 1.80 WHP

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2017

Games 1-54: 11 starts, 3.97 ERA, 1.37 WHIP

Games 55-108: 11 starts, 2.82 ERA, 0.99 WHIP

So, what was making the 2014 NL Rookie of the Year look so human in 2017? In short, he was throwing that electric fastball too much to righthanded hitters.

Through his first 11 starts over the Mets’ first 54 games, deGrom threw his four-seamer 50 percent of the time against righties, and his sinker — a useful variant of the straight heater — just 11 percent. Even the best pitchers can’t get away with throwing to major league hitters that are guessing fastball as if it’s a coin flip. In his next 11 starts (Mets games 54-108), he cut that usage against righties down to 38 percent, upping the use of his sinker to 23 percent. The results: righties hit .167 against his fastball and .194 overall.

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Tinkering with pitch usage can be an effective way to keep even the best hitters off balance, but it often comes at a cost. Throwing his sinker more allowed righties to hit .250 against it, considerably higher than the .182 in the first 54 games.

Much of that damage was mitigated by the way deGrom found a balance for his curveball/slider combination. Through game 54, he was throwing his slider 26 percent of the time to righties, while only mixing in the curveball six percent of the time. DeGrom’s slider is a force, thanks to how hard he throws it — a staple of any Dan Warthen disciple. But, his high usage of the pitch didn’t translate well. Righties hit .317 against his slider to start the season.

2017 Games 1-54 (11 starts)

Slider: 26% usage, .317 BAA against righthanded hitters

Curveball: 6% usage, .200 BAA against righthanded hitters

2017 Games 55-108 (11 starts)

Slider: 15% usage, .167 BAA against righthanded hitters

Curveball: 13% usage, .294 BAA against righthanded hitters

In games 54-108, deGrom started to work in the curveball more against righties, bumping its usage up to 13 percent and using the slider at only a 15 percent clip, a much more even split than 26/6. The results were drastic. Right-handed hitters only hit .167 against the slider, down from .317. They hit the curve 94 points better, but that compromise turned out OK. His ERA dropped down to 2.82, and his WHIP was 0.99, among the best 54-game chunks of his career thus far. This stretch contained almost all of his dominant starts in 2017. He notched a win in eight straight outings to tie a franchise record and worked deep into games to buoy a struggling Mets rotation.

DeGrom’s last two starts indicate he’s using the sinker more than ever, while reverting back to favoring the slider over the curveball. As the Mets languish near the bottom of the division and their ace tries to cross the 200-inning threshold for the first time in his career, the rest of the season may serve as the perfect test for deGrom to figure out just what combination serves his repertoire the best.