What To Expect From David Peterson In Cubs' Debut

The Chicago Cubs will send out newly acquired veteran left-hander David Peterson to the mound on Saturday in Game 2 of the three-game series against the Milwaukee Brewers. 

The Cubs traded for Peterson earlier this week in the wake of two more rotation injuries. They placed both Ben Brown (neck strain) and Edward Cabrera (hamstring/adductor strain) on the 15-day injured list on Wednesday, so the team needed some fresh arms. 

That led the front office to trade for a struggling southpaw in Peterson . The 30-year-old veteran owns a 6.09 ERA and a 19.7% strikeout rate across 68 innings pitched this season.

However, his expected numbers are much better than his actual numbers. With a 3.85 FIP and a 4.05 expected FIP, some positive regression should head his way within the next couple of weeks. 

So, what should Cubs fans expect from the new lefty in his Cubs debut?

Peterson will immediately come in and be tasked with trying to help the Cubs win their first game against the Brewers this season. The North Siders are 0-4 against their division rival so far, which included a 6-2 loss on Friday evening. 

Peterson will induce a ton of groundballs in this outing. He has always been a groundball pitcher and currently ranks in the 90th percentile in groundball rate (52.9%). That means Alex Bregman, Dansby Swanson, Nico Hoerner, and Michael Busch should have a busy night in the infield. 

The good news for both Peterson and the Cubs is that the team features plenty of former Gold Glovers in the infield. Bregman, Swanson, Hoerner, and Busch have a combined +21 Fielding Run Value in the first half. 

The southpaw leans heavily on his five-pitch mix to keep hitters off balance. He doesn’t throw hard with a 16th percentile average fastball velocity (92.2 mph), so Peterson has to mix up his pitches to keep hitters guessing. 

He doesn’t throw any of his pitches (sinker, slider, four-seam fastball, curveball, changeup) more than 30% of the time or less than 11%. He does a good job mixing up his pitches while posting an above-average 64.1% first pitch strike rate over the last three years. 

Peterson’s changeup is usually his best pitch. Opposing hitters batted .211 with a .324 slugging percentage and a 27.1% whiff rate against that pitch in 2024, and hit .223 with a .298 slugging percentage and a 24.1% whiff rate on that same pitch in 2025. 

However, hitters are all over his changeup this year, as they have a .355 batting average with a .484 slugging percentage and a 20.1% whiff rate. When Peterson’s changeup is working well off his other stuff, though, he can be a quality starter. 

Cubs fans shouldn’t expect Peterson to miss many bats with a 22.2% whiff rate and a 19.7% strikeout rate, but he will get a lot of groundballs and does a good job keeping the ball in the park. Both his barrel rate (6.8%) and pull air rate (13.5%) rank pretty well. 

If the Cubs are going to have any chance to win Saturday’s game against the Brewers, it will be on Peterson to give the team a chance to win.