We write pretty extensively about the problems with counting on a bullpen from year to year, They’re just far too volatile, inexplicable, and weird to know exactly what you might get from one season to the next. There might not be a better example than Blake Treinen.

Last season, Treinen was the most valuable reliever in the game. More than Edwin Diaz, more than Josh Hader, anyone. He ran a WHIP well under 1.00, struck out nearly 12 hitters per nine, and ran close to a 5-to-1 strikeout-to-walk ratio. He racked up 38 saves to backstop the A’s to the coin-flip game, and anchored a unit that was the backbone to that team as all their starters basically ended up looking like something out Walking Dead.

This year he can’t get anyone out.

He’s lost his closer’s job to Liam Hendriks. His Ks are down by nearly a third, and he’s doubled his walk-rates. His homers-per-nine is up 5x from last year. He only gave up two homers all of last season, and this year he’s surrendered seven that have landed in nachos or beer out beyond the outfield wall. He’s already given up as many hits this year as he did last, and there’s still more than six weeks to go in the season.

So what happened?

It’s not as easy to pinpoint as you might think for such a precipitous fall. Treinen has lost a smidge of juice on his fastball, but it’s only down slightly less than one MPH and is still averaging more than 96 MPH. That’s more than enough to get things done. What he can’t seem to do is throw it for a strike as often, as his strike-percentage with that is down about five percentage points. And that might be due to getting a lot more arm-side run on it, which is making it harder to control:

To go along with that, his slider has lost sweep as well, losing an inch of horizontal movement. We’ve said it before, but even though that doesn’t sound like a lot it’s the difference between a whiff and something fouled off or the latter and solid contact. Last season, Treinen got half the swings against his slider to be whiffs. That’s down to 34% this year. Hitters could only manage to even foul it off a quarter of the time. That’s 40% now, which means more pitches, which means more looks, which means worse results. If you’re StatCast inclined, his slider’s spin-rate went from 2, 735 RPM to 2, 597 RPM this year. He’s even scrapped more often for a cutter, which hasn’t really gotten better results.

Was it workload? Treinen threw 80 innings last year, the first time he had ever crossed that threshold, though he did throw 75 the year before that. Some pitchers can back up 80 innings year-t0-year, but you’d have to say Treinen isn’t looking like one of them. Hell, Hader threw 80 innings as well last year, and while he’s still been very good this year, teams have been able to get to him at points, which they couldn’t last year.

Of course, Treinen could discover something this offseason, get his slider sweeping again, and be the dominant monster he was in ’18. That’s the thing with relievers. Or at 32 next year, perhaps his time in the sun is forever gone. For this year, he’s leaving the A’s pen a tad short, though Hendriks has picked up the slack and Yusmeiro Petit along with Joakim Soria have picked up the slack as set-up men.

You can always think you know what you have in a bullpen. But you never really do. Unless you spend gobs of money like the Yankees. That’s not really an option for the A’s, so they’ll just have to guess again next season.