The Rays had an excellent bullpen in 2008. Their 3.55 bullpen ERA was fifth in baseball (even though Jason Hammel pitched 78 innings in a mop-up role and posted a 4.60 ERA, thereby raising the bullpen’s overall ERA). They had six pitchers in the top 72 in WXRL: JP Howell (6th), Grant Balfour (14th), Dan Wheeler (42nd), Troy Percival (64th), Chad Bradford (72nd) and Trever Miller (72nd). These six relievers combined to pitch 322 of the team’s 484 relief innings.

And every member of their strong bullpen is under contract for 2009 as well. This would seem to suggest that the Rays are likely to have a very strong bullpen once again in 2009.

However, if we look more closely at the numbers, we can see that some of the success of their relief pitchers is likely to be unsustainable.

The Rays had a fantastic defense in 2008, posting a DER of .710. Therefore, we would expect an individual pitcher on their staff to have a BABIP of approximately .290 (yes, there has been work done to suggest that some pitchers may have a small degree of control over their balls in play, but nonetheless we’d still expect most pitchers’ BABIPs to match their team’s DER).

With that in mind, let’s look at the Rays relievers’ BABIP, home runs per fly ball (HR/FB), and left-on-base percentage (LOB%).

Notice the absurdly low BABIPs for Balfour, Wheeler, Howell, and Percival. Each of these pitchers is likely to see his BABIP rise next season. Whil  Miller’s BABIP was rather high, his HR/FB was very low (average HR/FB is approximately 11%), and he is unlikely to maintain this low rate going forward.

Balfour too has a low HR/FB, and an extremely high LOB%. Some of Balfour’s high LOB% can be attributed to the fact that he was so dominant this year – whenever a batter reached base against him, Balfour was very likely to retire subsequent hitters and strand the runner. That being said, an 87.9% LOB% is absurdly high and unlikely to be maintained.

These numbers are reflected well in xFIP – a stat that corrects for random variation in BABIP, HR/FB, and LOB%. Let’s take a look at what these relievers’ xFIP was in 2008:

This confirms our suspicions: while some of these guys are very good pitchers, nearly all outperformed their xFIP – by a lot. Even if xFIP is underrating these guys for some reason (which, while possible, is not particularly likely), it’s unlikely that xFIP is underrating them by that much. In other words, it’s quite likely that these pitchers will see their ERAs rise in 2009.

The Rays have some quality pitchers in their bullpen – particularly Balfour and Howell. However, nearly all of their relievers benefitted from random fluctuation in 2008, leading to a bullpen that performed much better as a unit than we would expect. Look for the Rays bullpen to regress, perhaps significantly, in 2009.