Contreras’s Arm Slots

As Dave reported earlier on the cusp of last night’s waiver trade deadline the Rockies acquired Jose Contreras from the White Sox. As Dave noted this is a marginal move, sort of a tit to the Giants’s Penny addition’s tat, but, it does allow the Rockies to keep Josh Fogg out of the starting rotation in spite of Aaron Cook’s trip to the DL.

Contreras typically works from multiple arm angles. Dropping down to deliver some of his pitches. The pitchf/x data picks up release point and from it we can see an interesting trend.


These are the release points for Contreras this season. I split them by his August 19th start, because starting then he largely abandoned his lower delivery slot. The colors a little confusing, but the main point is that he throws all four pitches from his main arm slot and his slider and two-seam fastball from the second slot.

Here is what the movement of his four pitches looks like with the pitches from the lower arm slot semi-transparent.

The slider from the lower slot has less, and even negative, horizontal movement (negative movement is in to RHBs and away from LHBs). That means while his normal slider moves away from RHBs his dropped down slider moves in to RHBs. Hid dropped down two-seam fastball also moves in more to RHBs, and has less vertical movement, more ‘sink’.

I am not sure why he gave up pitching as much from the second arm slot. According to my numbers both the slider and two-seam fastball actually do better from the dropped down delivery (better run values). Among other differences the slider generates more whiffs from the dropped down delivery (30% versus 16% misses per swings) and the two-seam fastball way more grounders (56% versus 43% GBs per BIP). If I were Colorado I would look into having him bring back the second arm angle.

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Could be he’s hurting a little? That’s the reason I always dropped things like funky arm angles from my repertoire. It’s not unreasonable to suspect he’s throwing through a little bit of pain.