Who's our best relief pitcher so far this season?
Javier Lopez.
Yup, Javier Lopez.
How do I reach this conclusion? By checking WXRL. WXRL is a measure of the change in Win Expectation during a pitcher's outings above that expected from a Replacement-level pitcher, adjusted for strength of opposing lineups. Note that this metric gives great credit for holding tight late-inning leads and and even greater penalty for blowing those leads, even if runners left by other pitchers score the actual game-changing runs. It's who's on the mound that counts.
Here are the stats thus far for 2008:
| NAME | WXRL (Wins) | LEV |
| Javier Lopez | 0.77 | 1.15 |
| Hideki Okajima | 0.54 | 1.68 |
| Jonathan Papelbon | 0.50 | 1.77 |
| David Aardsma | 0.49 | 0.80 |
| Bryan Corey | 0.08 | 0.86 |
| Julian Tavarez | -0.28 | 0.34 |
| Kyle Snyder | -0.29 | 1.26 |
| Mike Timlin | -0.53 | 1.16 |
| Craig Hansen | -0.54 | 1.13 |
| Manny Delcarmen | -0.59 | 0.91 |
| Total | 0.15 | 1.00* |
The entire Boston bullpen, as a group, has been 0.15 wins better than a bunch of ten AAA call-ups thus far in 2008.
That's terrible. It's also probably not indicative of the bullpen's talent. Disregarding the stats of Corey, Tavarez and Snyder, all of whom are gone, raises the sum WXRL to 0.65, half a win better. We also know that we're taking a snapshot of Jon Papelbon at his worst moment: he would've been closer to 2.50 WXRL if not for those two fluke blown saves.
But flukes count in the stats.
Let's face it, relief pitching has been a problem for Boston in 2008. Let's also take heart in realizing that this is an area where we can expect to do much, much better the rest of the way, even without the Front Office's making a trade. Last year Papelbon, Okajima, Lopez, Delcarmen and Timlin were worth 13.3 WXRL over the course of the year. Expecting a third that much from the bullpen from now through September would mean a Boston team winning 99 games instead of the 95 games one might project from our current standings. Expecting just two-thirds of last year's production--expecting our relief pitchers to match, not to exceed, what they did last year--would result in 103 wins for Boston, all other factors held constant.
***
Our bullpen has sucked thus far. They're still good pitchers, though, and we're still a very good team.
* a leverage index of 1.00 defines the beginning of a game; the mean of Boston relief pitchers' LEV is different and less relevant.