Musing on Sergio Romo's Slider and Platooning

Hopefully Sergio Romo gets off the DL soon, because he is incredibly fun to watch.  Though Brian Wilson’s popularity might have you thinking otherwise, Romo is the original bearded reliever on the Giants.  He’s also the best reliever on the Giants.  He has an xFIP of 1.64, which would be lowest in the majors if his 37 ⅔ innings made the service time criterion.  His game is getting a ton of strikeouts while keeping his walks low - this year, he’s averaging over 12 and a half strikeouts per 9 innings while walking under ONE.  Unfortunately, he’s been sidelined recently with an arm injury that isn’t supposed to be too serious; he hasn’t thrown in a game since August 9th.  

 

Obviously, 30 is not a huge sample, but it’s clear that Romo hasn’t been comfortable locating his slider against lefties.  The graph (from the catcher’s perspective) shows the density of pitches that cross the plate on the outer half of the zone or off the plate away.  They’re against righties, who will see the pitch cutting away from them.  Against lefties, however, he’s forced to backdoor it.  That can be fine if he keeps it on the outside corner, but that location takes away the bat-missing abilities it has against righties.

So, even though it may not seem reasonable to cut such a successful pitcher’s playing time so much, I don’t think it’s an outrageous move at all to reserve Romo for (mainly) right-handed competition.  That way, he can use his slider most effectively.

The data here are courtesy of Joe Lefkowitz's PITCHf/x tool.

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This will be my last piece as a featured writer for Beyond the Box Score.  I would like to thank my co-writers here at BtB for being such supportive teammates and overall good-guys, and a particularly big thanks to Justin for, honestly, everything.