A Deep Dive Into A.J. Puk's Splits Reveals an Encouraging Development

Puk could be a very big left-hand weapon for Diamondbacks manager Torey Lovullo late in games, especially with a change that has been paying off in 2024

Jul 6, 2024; Miami, Florida, USA; Miami Marlins relief pitcher A.J. Puk (35) pitches against the Chicago White Sox during the eighth inning at loanDepot Park. Mandatory Credit: Rhona Wise-USA TODAY Sports / Rhona Wise-USA TODAY Sports

The Diamondbacks traded on Thursday, acquiring left-hand pitcher A.J. Puk from the Miami Marlins in exchange for minor league slugger Deyvison De Los Santos, and outfielder Andrew Pintar.

Mentioned in our article, and discussed widely throughout the internet, television, and radio airways, was the fact that Puk has much better numbers as a reliever in 2024 than he did as a starter. Those numbers were extreme. In 13.2 starter innings, he allowed a 1.105 OPS and had a 9.22 ERA. In 30.1 relief innings, he has just a .456 OPS against and a 2.08 ERA.

As we like to do here at Arizona Diamondbacks On SI, let's dive a little deeper, shall we?

To begin with, we need to widen our sample size a bit. 30.1 innings of relief is just not that many. It's always difficult with relievers, but we can get a little better handle by increasing the sample size. In this case, we are looking at all relief innings thrown by Puk from 2022 through 2024.

Over that time span Puk has faced 637 batters and thrown 153.1 innings. He has a 3.23 ERA with a 3.40 FIP. The batting line against is .216/.282/.362, .644 OPS against. He has a 187 strikeouts, 42 walks, and 19 homers. Those are very good numbers overall, although he's been somewhat homer prone. More on that down below.

It becomes more interesting when we look at the handedness splits. One thing is evident. Puk is a lefty killer. Standing at 6'7" tall, he gets on top of left-hand batters with mid-90s fastballs and a combination of sweepers and sliders. Here is the line against left-hand batters as a reliever since 2022:

220 BF, 57.1 IP, 1.88 ERA, .165/.230/.275 , .505 OPS, 74K, 8 BB, 6 HR, 2.84 FIP

That's about as good as it gets. He is a real weapon out of the pen and will be used against the toughest lefties in the toughest situations. Of course, that will mean plenty of chances against the best left-hand batters in the league, who can handle left-side pitching. But it's still going to have a neutralizing effect more often than not.

Puk will still face right-hand batters two-thirds of the time. While Torey Lovullo will surely look to optimize him in parts of opposing lineups that will be more advantageous, teams will pinch-hit whenever they can. Here is Puk's line against right-hand batters in relief:

417 BF, 96 IP, 4.03 ERA, .243/.309/.408, .717 OPS, 113K, 34 BB, 13 HR. , 3.73 FIP

Those numbers are roughly MLB average. The biggest issue in this sample, underlined above, is the homers allowed to right-hand batters. But there is a really encouraging sign coming out of his 2024 numbers that indicates he might have corrected this issue.

Nine of those 13 homers came on four seam fastballs prior to 2024. Puk has not allowed a homer on a fastball to a RHB this year, either as a starter or a reliever. Four came on sliders, two of them this year.

This is a very big development for the big left-hander. Not having had a chance to speak with him yet, it's impossible to say what changes he may have undergone to get these results. Whether it's sequencing, location, a grip change resulting in a slightly different movement profile, or just plain luck, is something we'll continue to dive into.

Mike Hazen made it clear on his media call that the team felt they were lacking a power lefty to get big outs in high leverage at the back end of the bullpen. Puk fills that need. Being under control for two-plus seasons was another factor Hazen highlighted.

Hazen said he was not blind to the fact that he paid a steep price to acquire Puk. 21-year-olds dominating in AA and AAA with big-time power are not common. But you can't acquire a good player by trying to sell the other team on players that are having bad seasons or not well known, Hazen said.

The D-backs had a need. They went out and filled it, and they should be a better team for it.