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Brad Boxberger is throwing what?

(A pretty good slider.)

MLB: Texas Rangers at Tampa Bay Rays Kim Klement-USA TODAY Sports

Brad Boxberger is a question mark for Rays fans, and has been for a while now. After bursting onto the scene with an absurdly dominant season as the setup man in 2014 (42% strike rate(!), 8% walk rate, 2.37 ERA, 1.95 xFIP), he regressed, painfully and in high leverage situations, as the closer in 2015 (27% strikeout rate, 12% walk rate, 3.71 ERA, 4.00 xFIP).

Then he lost most of his 2016 season to a core muscle injury that required surgery, and lost the first half of the 2017 season to a lat strain and a flexor strain.

With such a wide range in performance and so much time missed, I’m not sure anyone quite knows what results to expect from Boxberger going forward. I certainly don’t. But there’s something unexpected going on in his process as well that it’s time we start paying attention to.

That’s a slider. Brad Boxberger, the standard bearer in the Rays succession of dominant fastball-changeup combinations, is throwing a slider.

He actually started throwing it last year, and he threw it before coming to Tampa Bay. Here’s the progression, with each data point representing one months.

Boxberger threw a slider as his third pitch in San Diego, but shortly after joining the Rays he dropped it entirely. That’s essentially the same trick pitching coach Jim Hickey played with Fernando Rodney:

  1. Acquire a pitcher with one of the best changeups in baseball, but who is hampered by poor command.
  2. Have him simplify his approach by focusing on how the the fastball and the changeup work off each other.
  3. Possibly do other clever things (like moving Rodney to the other side of the pitching rubber, or by making changes in mechanics that nerds like me who never played the game don’t notice).
  4. Get lucky and enjoy one of the best reliever seasons ever.

As you can see in the graph above, Boxberger did actually work his slider back into the mix after coming off the disabled list last year, but honestly, it wasn’t very good. If the 2017 version looked the same as the 2016 version, I’d right now be confidently advocating that he scrap it again, and try go back to that 2014 magic.

But let’s pause that train of thought and look more closely at the 2017 slider version:

  • Using the Brooks Baseball classifications (MLBAM has a few misclassified), Boxberger has only thrown 13 sliders, so we’re not working with much. Caveats.
  • This is a hard slider. Boxberger’s velocity on the pitch is up from last year, to 87.1 mph. League average is 84.4 mph, and Boxberger’s mark is more than a full standard deviation above that. For Rays reference, Chris Archer’s plus-plus slider averages 89.2 mph, or two standard deviations faster than average. So Boxberger isn’t Archer, but he’s still throwing hard.
  • Generally, there’s a tradeoff between velocity and movement, particularly vertical movement. The thing that makes Archer so special is that he throws his slider extremely hard, but it still drops slightly more than the average, much softer, slider. Boxberger isn’t quite at that level, but once more, he does pretty well. His average vertical rise of 1.8 inches is only a third of a standard deviation more than the league average. So to synthesize the two, Boxberger’s slider has good vertical movement for its velocity.
  • I’m less sure what to say about horizontal slider movement than I am about the relationship between speed and vertical movement, but just to note it, Brad Boxberger’s slider runs away from a right handed batter more than is average.
  • I actually suspect that Boxberger’s slider has the potential to be more live than the averages I’ve stated above give him credit for. Look back at the first graph. There are a few sliders on there that simply didn’t drop. Those are hangers. The main clump sits down near the zero mark on the y axis. So rather than just having good drop for its speed, this may be a pitch that, if Boxberger gets a better feel for it, can actually be a hard slider with above average drop.

Thirteen pitches is too few to consider results, but the results have included two whiffs and one home run. Based on the movement, I’d expect the whiffs to continue. Based on Boxberger’s suspect command and high career home run rate, dingers are maybe a safe bet also.

It does seem like a strange idea for a reliever who once struck out 42% of the batters he faced on the strength of just two pitches to work on reintroducing a third. The more intuitive blueprint would be to stay simple and work on repeating his delivery in the hope of getting back to that 2014 level.

But observed performance isn’t necessarily true talent, and true talent isn’t something that stays at the same static level throughout a player’s career. Brad Boxberger and the Rays try to get better all the time, and right now they seem to think that means working in a potentially above-average slider.

Hope they’re right.