David Peterson Has Melted Right into Cubdom, Thanks to Changes That Started with Mets

When the Cubs traded for David Peterson late last month, it was as much out of desperation as out of proactivity. True though it was, Jed Hoyer's asseveration that the team had had interest in Peterson already didn't mean they actually would have pulled the trigger when they did, but for the massive injury trouble that struck their starting rotation just before the trade. With Ben Brown and Edward Cabrera landing on the injured list simultaneously, they needed a warm body and a working arm. They couldn't afford to be especially picky.

Count them lucky, then, as well as good, because in Peterson, they found the right stopgap to fit their needs not only in the moment, but for the balance of the season. He's no more than a backend starter, but he's also no less than one, whatever his numbers in a brief and cursed start to the season with the star-laden and star-crossed Mets might have implied. Moreover, his stuff suits the Cubs' predilections gorgeously—and just before they acquired him, he made some changes that made him even more perfect as a prospective Tommy Hottovy pupil.

Peterson's four-seam fastball has natural cut, which the Cubs have long loved. However, he also has a good sinker, and he tends to lean on that more heavily when he has a good feel for it. The two pitches work well as a tandem, not because of the way they play off each other, but because the four-seamer's unique shape sets up his fading changeup, while the sinker can prime hitters to misread and mishit his breaking stuff. However, he ran into major alignment problems early in the season with the Mets, which left him unable to locate either hitter well enough to set up much of anything. Since neither offering is thrown especially hard or has lively enough movement to make up for that, their newfound failure to help the other pieces of his repertoire play up became a huge problem.

The fix, however, was simple—so much so that even the Mets figured it out. About a week before he was dealt to Chicago, Peterson moved from the center of the rubber to the third-base side. Here are side-by=side looks at him mid-delivery at Wrigley. One shot is from when the Mets visited the Cubs early in the season, and the southpaw was working on behalf of the visitors. The other is from his start against the Tigers Tuesday night, in which he pitched 6 2/3 impressive innings in a breezy Cubs win.

Sliding over toward the side to which (relatively speaking, and to the eye of the hitter) the four-seamer already wants to move has made it much easier for Peterson to target the up-and-in quadrant against right-handed batters. That's extremely valuable; God hasn't yet created the hitter who feels comfortable when a pitcher can spot the ball there. 

Working along the entire top rail of the zone, as Peterson was doing before he came to Chicago, sounds good in theory. In practice, with a fastball that has neither good rising action nor average-or-better velocity, it left him running into barrels too often. Being able to force that pitch to the glove-side half without losing the height on it is a cure for that condition, and moving over on the rubber has been enough to accomplish it.

Meanwhile, the sinker—in fact, let's call it a two-seamer; it's much more of a runner than a heavy, dropping pitch—can be thrown with more conviction and action now. Being closer to the glove-side edge of home gives Peterson more real estate with which to work. He can let the two-seamer run a bit more, which makes him harder to square up.

That change in starting position happened before he joined the team, but Peterson has also tweaked his approach to suit the shift, and that adjustment has a more distinctly Cubs flavor. In his first several appearances for the team, Peterson threw more sinkers than he did in most of his appearances with the Mets this year. He leaned into the pitch he already had the best command of. However, Tuesday night against a heavily right-handed Tigers lineup, that changed. Peterson went to the four-seamer more, and found even more success.

There's nothing more to unlock here. Peterson won't be an ace, no matter how he continues refining his approach under the Cubs' tutelage. He can be a very good mid-rotation arm with this team, but even if so, he'll owe much of the credit to the excellent Cubs defense. Still, what he can be is plenty for this team, which has gotten a bit healthier in the rotation since acquiring him and which figures to add another starter in the next 10 days. Peterson was already a Cubs-coded hurler and made the most important changes needed to get back to his best self before the club even dealt for him. Now, he just needs to execute each time he takes the mound, and keep trusting both his coaches and his on-field support staff, the defense.