Ranking the best relievers in baseball

Remember the Ultimate Pitcher Rating exercise from a few days ago? The idea was to take K/BB ratio and GB/FB ratio and multiply them together as a measure of the way a pitcher maximizes strikeouts and ground balls and minimizes walks. (Credit should be given to work done by Ron Shandler and others -- I'm certainly not pretending to be the first person to think this way.)

You can do the same thing with relief pitchers. In some ways, relief pitchers have a job that's different than that of starting pitchers -- for one thing, they often inherit runners that must be stranded. But the basic premise is the same: Get as many outs as possible. The more hitters a reliever strikes out and the more ground balls he induces, the more outs he's going to get.

Check out the relief pitcher leaderboard from 2008:
1. Mariano Rivera, 22.71
2. Jonathan Papelbon, 15.22
3. Chad Qualls, 9.97
4. Rafael Perez, 8.79
5. Carlos Villanueva, 8.55
6. Cla Meredith, 7.89
7. Matt Thornton, 7.82
8. Hong-Chih Kuo, 7.62
9. Brian Shouse, 7.53
10. Jeremy Affeldt, 6.30

(Note: Rivera and Kuo both had sub-2.00 ERAs, while Papelbon, Qualls, Villanueva, Thornton and Shouse all had sub-3.00 ERAs. Of the top 10 relievers in what we'll call Ultimate Pitcher Rating, only Meredith had an ERA over 4.00. That ought to tell you something about the validity of the statistic.)

Here's what the leaderboard looks like this year:
1. Mariano Rivera, 26.70
2. Chad Qualls, 20.39
3. Scott Downs, 12.09
4. Bobby Jenks, 8.90
5. Todd Coffey, 8.13
6. Jonathan Broxton, 8.09
7. Jeremy Affeldt, 7.81
8. Pedro Feliciano, 7.67
9. Joe Nathan, 7.39
10. Manny Corpas, 6.32
***
26. Justin Masterson, 4.80
(Daniel Bard does not qualify but would rank 56th at 2.82.)
87. Manny Delcarmen, 2.03
108. Hideki Okajima, 1.65
122. Jonathan Papelbon, 1.39
124. Ramon Ramirez, 1.36
134. Takashi Saito, 1.18

You might be right to be worried about the Red Sox bullpen, a group of pitchers that has looked more and more mortal as the summer has progressed. Check out the unit's ERA by month so far this season:
* April: 2.88
* May: 3.04
* June: 3.82
* July: 4.00

The Ultimate Pitcher Rating stats show that the unit might be regressing to the mean and not just going through a slump. Check out Papelbon's peripheral numbers over the years, just as one example:

K/BB
2006: 5.77
2007: 5.60
2008: 9.63
2009: 2.28

GB/FB
2006: 0.82
2007: 0.52
2008: 1.58
2009: 0.61

Papelbon's strikeout-to-walk numbers are way off his career norm, and his ground ball-to-fly ball ratio, while in line with what he did in 2006 and 2007, has dropped steeply from 2008.

At one time, it looked as though the Red Sox would be able to cruise into the playoffs with the best bullpen in the game. Now, though, they're showing chinks in the armor -- and the numbers say those chinks might be evidence of real weakness.

(The solution? According to these numbers, Chad Qualls of the last-place Arizona Diamondbacks might be the second-best relief pitcher in baseball behind Mariano Rivera. He's arbitration-eligible after this season and a free agent after the 2010 season. Go get him, Theo. Go get him.)