Keegan Thompson Found 3 Miles Per Hour on the Shuttle from Des Moines to Chicago

It's hard to fathom the leap in stuff Keegan Thompson has effected since he re-joined the Cubs' active roster amid injuries that have taxed the bullpen in April. Maybe Thompson was dealing with a nagging, undisclosed injury when he started this season in Triple-A, not looking like he belonged on a big-league roster. Maybe he was experimenting with ways to pitch that would protect him from such an injury, and that just meant throwing less hard (among other things). Maybe he and the Cubs' big-league coaching staff discovered a mechanical tweak that was available to him, which his instructors in Iowa hadn't caught. 

Whatever the case, Thompson is a radically different pitcher right now than he was three weeks ago, when he was a minor leaguer and looked like he might never be much else again. We're not talking about a slight uptick or a tradeoff that got him more velocity at the cost of some other characteristic. Thompson's heater has transmogrified since he put the big-league jersey on for the first time.

He's yet to throw a fastball in MLB as slow as his fastest one in Triple-A this year. His spin rate is back up to where it was when he was going well. He has more riding action on the pitch, from a lower release point, which is giving him a flatter vertical approach angle. He's even getting slightly better extension toward the plate at release, making his fastball play a full three ticks faster than it did in the minors.

Thompson's whole arsenal has changed, in fact. He's reintroduced his slider, and the relationship between his four-seamer, cutter, and sweeper is restored to what it needs to be for him to succeed. Here's how his pitches were moving with Iowa.

And here's what they've done since he joined the parent club.

Thanks partially to more consistently achieving the spin he wants and throwing it with more conviction, Thompson is also commanding the fastball much better. It's the pitch with which he attacks the top of the zone, and off of that tunnel, everything else in his arsenal plays up. The locations at which he threw heaters in Iowa betray a lack of a cohesive plan.

But we've seen him much better utilize the upper half of the zone and attack hitters with the deception that creates, while he's been in MLB.

If I had to guess, I would hazard that the team and Thompson did make a slight alteration to his arm slot. He's always had the kind of arm action that depends on great proprioception to permit command, because of the way he tilts his spine and lets himself lean toward the first-base line as he delivers. It's unlikely that he made a sudden and massive leap in functional core strength, which is one way to improve command and power in such a delivery, but if he and the coaches found a cue that lets him more confidently execute his motion and repeat his release point and hand position, it would explain a lot of what we've seen since he made it back.

This version of Thompson, with bilateral command of the heater across the top of the zone; the curveball working off it against lefties; the sweeper doing the same against righties; and the cutter he can manipulate a bit to use against either type of hitter, is a very good pitcher. It's miles different from the guy we saw most of last season, and from the one who was throwing such tepid, scattershot stuff early this month.

It would be foolish of the Cubs to rest on their laurels after reviving their erstwhile bullpen stud. He's still more solid than spectacular. The relief corps will still need further reinforcement, and Thompson shouldn't be treated as a relief ace. He's earned a shot to be a medium- to high-leverage option, though, by getting back the sizzle on his fastball and reminding the organization of what made him such a versatile weapon for their pitching staff in 2022. If he can keep throwing this hard and show this kind of command with such a deep arsenal, he's even a candidate to make some starts (or longer relief appearances) as the marathon that is the regular season unfolds.