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Short Musings on the Giants’ Bullpen

July 22, 2010

There’s been some talk lately about the Giants needing to add a reliever by the trading deadline, and I agree with this sentiment.  I am not, however, of the state of mind that a move for a bullpen arm is imperative- this is because reliever performance is, by and large, volatile.  But I thought I’d take a short look at the current state of the bullpen, before any acquisitions are made.

First, how is Bruce Bochy handling his relievers?  Below is a chart that gives us a sense of which relievers he trusts the most in tough spots.  If you’re unfamiliar with Leverage Index (LI), keep in mind that an LI of 1.00 is an exactly neutral game state.  Game LI (shown as gmLI) is a pitcher’s average leverage index when he enters the game.

As the chart demonstrates, certain players are being “trusted” more than others.  Pitchers Waldis Joaquin, Denny Bautista, and Joe Martinez have all acted in the capacity of “mop-up” men, appearing mostly in games with very little pressure.  Mota and Runzler are your classic middle relief arms, with Ray right around there as well- and then we see the most trusted relievers: Romo, Affeldt, Wilson, and Casilla.  Wait, Casilla?  That’s right- Bochy has been putting Casilla in some very critical situations this year.  This is partially offset by the lack of innings pitched, but it appears that Casilla is essentially Bochy’s “specialist.”  Now, how about their performance?

Ray’s had too few innings pitched to show any real signs of anything, but Brian Wilson leads the pack (as expected from your ace reliever) with a .290 wOBA against (all wOBA figures shown use coefficients generated to match the Giants’ runs allowed environment, rather than the National League’s).  Denny Bautista has been pretty solid, followed by Sergio Romo.  “Specialist” Casilla hasn’t been very good, as the average wOBA for the Giants’ pitching staff is .324.  Now, let’s convert this into runs above/below average, and then multiply by the player’s gmLI.  This will give us an idea as to which pitchers have been particularly good (or bad) to the Giants’ staff, because we’re now accounting for the difficulty of the game state:

Remember how the earlier chart told us Affeldt was pitching in the second-toughest situations of primary relievers?  Yeah, that’s not working out too well.  Affeldt’s getting hit rather hard this year, and I’d be hesitant to continue allowing him to pitch in such tough spots.  As I said before, though, reliever performance is rather volatile, and it’s certainly possible (although maybe not probable) that he’ll regain some success in the latter innings.  But for the time being, I wouldn’t trust him in those high leverage spots.  Let Romo become the primary setup man, and try and work out a deal for another reliever to help solidify the late innings, unless Chris Ray returns to form.  Having two reliable relievers in Wilson and Romo just isn’t enough.

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