Under The Knife 5/26/26

Under The Needle, Under The Gun

FERNANDO TATIS JR, OF SDP (no listed injury)

I had started researching Fernando Tatis Jr.’s disappearing power over the weekend because the underlying metrics didn’t match the outcomes. The bat speed is still elite. The exit velocity remains comfortably in the range of the version of Tatis that used to launch baseballs into the second deck. Yet the actual damage, especially on pulled fly balls, has vanished in a way that didn’t feel random. My first thought, naturally, was his surgically repaired shoulder might be acting up again.

Tatis spent much of 2021 playing through repeated instability in his left shoulder before eventually undergoing stabilization surgery after the season. Players can come back structurally sound from those procedures and still carry movement adaptations years later. One hitting expert I trust put it perfectly: “When you can’t ‘finish high’ in your follow-through, it can result in ‘coming across the zone flat’ which could be the root cause of Tatis’s very low pull side launch angle results so far this season.” That immediately clicked with what I was seeing on video and in the data.

Then Driveline went deeper and essentially arrived at the same intersection from a completely different direction. Travis Sawchik’s forensic breakdown focused heavily on the flattening of Tatis’s pull-side launch profile despite maintaining excellent bat speed and impact quality. They weren’t really diagnosing the shoulder. They were diagnosing the swing, but the fascinating part is how closely the two conversations align.

Where I think caution still matters is causation certainty. Baseball people love finding one elegant answer for complicated movement patterns. The shoulder may absolutely be influencing the bat path, consciously or subconsciously. Hitters protect vulnerable joints in ways even they often don’t realize. Movement adaptations also become layered over time. Sequencing changes. Timing changes. Swing decisions evolve. Sometimes the body solves one problem while quietly creating another.

Still, the overlap here is difficult to ignore. Tatis looks like a hitter whose rotational freedom through the finish is different than it used to be. Not weaker. Not slower. Just different. That’s what I’d watch moving forward. Not just whether the home runs return, but whether the finish does. Does he start getting the barrel out front and uphill again on pull-side contact? Does the follow-through look freer and higher? Does the swing stop cutting across the zone so flatly? The data and the medical history are increasingly telling the same story, just in different languages. For Tatis, he’s got other things on his mind, I’m sure.

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