Why Chicago Cubs Targeted David Peterson to Patch Their Porous Rotation

[Matthew Trueblood]

Image courtesy of © Kyle Ross-Imagn Images

You don't have to squint to see David Peterson's appeal for the Chicago Cubs. Firstly, look at that pulse! You won't find it on the Savant sliders panel, but being a living, breathing pitcher who isn't injured is a tough box to check these days, it seems, and the Cubs found a guy who checks it. More seriously, though, Peterson is a lefty who throws 92 MPH; succeeds by missing barrels, not missing bats; and was available in a buy-low deal, despite the calendar not yet having flipped to July and most could-be trade partners still being focused on preparations for the draft. When Ben Brown and Edward Cabrera landed on the injured list simultaneously (with no imminent return looking likely for either), Jed Hoyer did what he had to do.

That doesn't mean that Peterson was selected solely because of his availability, though, or even because of the natural cut on his four-seam fastball. Rather, the Cubs locked in on him because there are real reasons to believe he's better than the ugly 6.09 ERA he's posted in 16 appearances (only half of them starts) this year. 

First, let's talk about what's gone wrong. To do so, we can look at Statcast's new swing timing metrics, to spot the ways in which hitters are reacting differently to his stuff this year than last. Peterson's best pitch is his sinker, but that offering (his ticket to last year's All-Star roster) is getting pummeled in 2026. Against lefties, the problem seems to be a failure to bust them inside and get them to hit the top half of the pitch, as you can see most clearly in the righthand image below:

Against righties, the problem is that Peterson hasn't been able to get batters looking up or in, thereby incuding contact off the end of the bat when he goes to the sinker. Instead, righties are centering that pitch up relentlessly.

Peterson actually throws his four-seamer more than the sinker to righties, a sensible practice for any non-fireballing southpaw. This year, though, righties aren't fooled by that, either.

He's actually getting in on the label with that cutting four-seamer a bit better than in the past, which could be good news. Unfortunately, paired with the batter being on time more consistently, rather than late, it's yielding good results for the batter, not for Peterson. 

When he's right, Peterson's slider is also a solid pitch, working across the plate to lefties and dipping below what a righty batter thinks they have lined up. This year, none of that is happening.

A good left-on-left slider should have an opposing batter reaching, flailing, way early and over the top of the pitch. Peterson just isn't producing those swings nearly as well this season as he did when he had a small star turn last year. At this moment, it's fair to say that hitters have him figured out a bit.

The Cubs can help him, though. For one thing, Peterson's slider is very much a gyro-style tight spinner, but it's taken on an unwelcome cement-mixer quality this season. He's throwing the pitch harder, but partially because of that, it's moving less. It has some dart to it, but it's lost depth. Here's the spin profile of his pitches for 2025, with the initial spin direction on the left and the actual movement direction on the right.

Here's the same image for 2026:

Peterson's slider feels much more like a cutter this year, and the result is a pitch that doesn't dominate lefties as well. If it looked a lot like the sinker and/or the four-seamer out of the hand, it could at least fool batters that way, but it does that (if anything) less well than a year ago.

That seems like something a new pitching coach can help a pitcher restore in short order. A small mechanical fix might go a long way for Peterson. Even better, though, the Cubs have one of the league's best defenses to offer Peterson. He's had a below-average strikeout rate in each of the last three years, but he keeps the ball on the ground often and in the park nearly always. The Cubs saw, up close, just how bad the Mets' defense has been all season. The jump from that to the Cubs' phalanx should be very good for Peterson—and what's good for him will be good for the team.

The upside on this acquisition is extremely low. Peterson will be a free agent this fall. He doesn't pound the zone the way you'd like to see a pitcher who doesn't strike batters out do so; that's part of his strategy to limit the damage done against his highly hittable stuff. He can't save the Cubs' season. If it's to be saved, that will be done by the team's offense and its defense. Peterson is a couple small adjustments from regaining the much better results he enjoyed last season, though. A restored slider would give him an edge in the fight to get batters off the barrel on his sinker. A bit of counseling from Tommy Hottovy should help him see a better way to utilize that cutting four-seamer in on righties.

Mostly, Peterson needs to soak up innings. But the Cubs didn't grab him just to get those innings out of the way. They believe, rightly, that they can get him back into the shape of a credible backend starter, and that would check several boxes at once on the North Side.

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