As you may have heard/read/seen, the Angels completed their search for bullpen help yesterday, acquiring lefty reliever Joe Thatcher for mid-level outfield prospect Zach Borenstein. While it’s plainly evident the Halos needed an additional arm to bolster the bullpen, I’m not convinced that pitcher had to be a LOOGY like Thatcher.
The platoon advantage is a well-understood and widely accepted concept, and the ability to employ that strategy on offense certainly pays dividends over the long haul. Just ask Billy Beane. What is a bit more nebulous is whether or not the same payoff exists for teams who combat the strategy by putting relievers in to face one or two batters at a time.
There is no doubting that LOOGYs like Joe Thatcher are successful at handcuffing lefty hitters. Where the doubt creeps in is in wondering whether that success really creates much value over the course of a season—or in Thatcher’s case, half a season. The top tier of LOOGYs and ROOGYs seem to average between 50 to 75 appearances a year—fairly hefty numbers—but those outings don’t tend to add up to much in terms of actual innings pitched. Thatcher, for instance, topped out at 45 innings in 2009, and has averaged just 30 innings a year over his seven full seasons of MLB ball.
Can you imagine Garrett Richards being limited to five or six starts the entire season? That’s essentially the upper limit for specialists like Thatcher. Knowing that, it’s easy to see why Thatcher has accrued only 2.5 WAR over his seven-plus year career; there’s only so much value one can add when his opportunities are so limited. That’s not to say he doesn’t add anything at all to bullpen, but it’s important to question whether the marginal value he creates is worth taking innings away from guys like Joe Smith and Mike Morin—i.e. the team’s best relievers. Would they really perform that much worse in the same situations? Probably not.
By going out of their way to acquire Thatcher, the Angels have essentially conceded that they cannot build a reliable bullpen without having a lefty in the mix. But that’s simply not true. For the 2011-2013 seasons, I looked at the percentage of relief innings each MLB team gave to its lefty arms* and found no relationship whatsoever between their increased usage and a bullpen’s overall success (ERA, FIP, or fWAR). The r-squared correlation for ERA and FIP were essentially zero, and while fWAR—which has FIP baked in—did show just the slightest glimpse of a positive relationship, it’s nowhere close to being meaningful.
*For example, the Angels had lefty relievers throw 76 1/3 of the bullpen’s 493 2/3 overall innings last year, so their percentage was a little on the lower end at 15.46%.
Several teams have found success by having lefties take a large chunk of relief innings, but so too have teams who didn’t. The 2011 Milwaukee Brewers had one of the league’s best bullpens, but gave only 29 of its 449 2/3 relief innings (6.45%) to lefties. The Red Sox (7.4 WAR) and Yankees (6.6 WAR) also found bullpen success with minimal LOOGY usage—17% and 12.5%, respectively—that season. The methodology here is admittedly crude, but its message is clear: It’s much more important for a team to simply use its best arms than worry about having some semblance of lefty/righty balance in the ‘pen. If you have a solid lefty, great, but if not, it does no good to force the issue.
For evidence of this, one needs to look no further than the heyday of the Angels’ relief corps in the mid-2000s. In 2004, the bullpen put up a franchise-best 8.3 WAR over 490⅓ innings. You know how many of those innings were thrown by a lefty? Two. As in one more than one.
This year, the Halos have used six different lefty relievers to cover 17 innings, and the results have not been pretty. They’ve allowed 15 runs, 21 hits, and walked 12 in that span, resulting in a cumulative -0.5 WAR. Having a lefty in the ‘pen just for the sake of having one has hurt the Angels this year.
All this isn’t to say that Thatcher won’t help the team down the stretch—I’m pretty confident that he will. What it does say is that the club might have gotten even more help by merely going after the best reliever available rather than limiting themselves to one of the best lefties. Acquiring Huston Street and/or Joaquin Benoit wouldn’t have come without some added cost—Borenstein alone wouldn’t have cut it—but one can certainly argue it would have given the Halos more bang for their buck. Not only have both pitchers averaged double the workload of Thatcher on a per-season basis over their careers, but they also have a whole other season of team control from which the Angels could have benefited.