On the back of James Wood and MacKenzie Gore having a great weekend after their recent slumps Bluesky user kelseylobster requested that I do a similar post about Mitchell Parker. And since I am a strong subscriber to the principals of service journalism, I must obey.
Parker makes sense as a target for supernatural improvement in fortunes because boy have they turned against him this year. After a surprisingly successful rookie season where Parker seemed to establish himself as a solid 4th/5th starter with a 4.29 ERA and 112 DRA- he’s taken a massive step backwards, risking any future with the team.
The big difference is in his strikeout rate, going from a fine, but workable 20.6 percent in 2024 to a disastrous 14.5 percent in 2025. That puts a lot more pressure on the defense to make up the outs and the Nats defense is definitely not up to the task.
Parker has four pitches he offers a low 90s fastball, a mid 80s splitter, a mid 80s slider (some call it a sweeper), and a low 80s curveball. The two that have given him the most trouble this year are the fastball and the splitter.
Parker’s fastball averages a solid 18 inches of induced vertical break (IVB), gravity defying movement that should be making it harder to hit. However, because of his extremely vertical release point with a 63 degree arm angle, the fastball only has a vertical approach angle of -5.3 degrees, making it pretty hittable. Parker had similar issues with his fastball last season but has exasperated them by increasing his arm angle by 9 degrees from 2024.
Parker suffers from a similar, but opposite, problem with his splitter. Unlike the fastball, Parker’s splitter has pretty terrible induced vertical break at 9.2 inches, well above the league average of 3.2 inches. In other words, Parker’s splitter does not do the one thing a splitter is supposed to do, break downwards.
While this was a problem last year too, when it had 8.3 inches of IVB, paired with his increased arm angle it was enough of a change to completely ruin his location of the splitter. On the left is a heatmap of his splitter locations in 2024, on the right is his splitter location in 2025.
A pitch that’s supposed to be getting swings-and-misses and groundballs at the bottom of the zone is now ending up in the middle where it can be blasted, with the expected wOBA on contact for Parker’s splitter jumping from .302 last season to .384 this year. Unsurprisingly, in response Parker has decided to significantly reduce the use of his splitter going from around 20 percent at the start of the year to 5 percent.
For a pitcher who already struggled with deception, completely dropping a pitch from his arsenal is not going to help in the long term. Parker would likely benefit from two changes: reducing his arm angle and finding a changeup grip and shape that works for his throwing style.
At the very least the first change should put him back in the arm slot that he had more success with in 2024. Ideally though, Parker would spend this offseason working on an even lower arm angle that can give him a better chance to turn the IVB of his fastball into a real weapon that can generate more than the 10 percent whiffs that he currently gets from it. While a lower arm angle is not automatically better, many highly successful pitchers like Logan Webb, Sean Manea and Zack Wheeler have found lowering their arm angle dramatically improved their outcomes. It won’t be an easy change, but with how bad Parker has been this year, I think it’s a worthwhile pursuit.
The second change would give him a bridge pitch between his fastball and breaking balls that increase all of their deceptiveness. Right now, because Parker has shelved his splitter, it’s pretty easy for hitters to identify the fastball versus the hard breaking slider and curveball. With the proliferation of data on the relationship between pitcher mechanics and pitch shape a new Nationals coaching staff should be able to help Parker identify the right pitch to replace the splitter, give him a new weapon, and get his groove back.
Overall, Parker’s situation highlights the Nationals need for better coaching and player development staff that can identify these problems earlier and work with him to fix them. That also means he could end up being a good test case for the next Nationals front office and coaching staff to see if the team is truly taking the steps needed to catch up with the rest of the league.
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