Simply because of their importance, number of innings thrown and less volatile nature, entire starting rotations are rarely ever around replacement level. The same is not true for bullpens which can be torpedoed by a fewer poor performers and also because managers tend to display a level of loyalty to relief pitchers that is unjustified given how much variance they display in performance from year to year.
Last season saw both the Pirates and Nationals have their collective bullpen be worse than replacement level. To date in 2010, the biggest team culprit in the bullpen failure Olympics has been the Arizona Diamondbacks. The unit’s 1.24 strikeouts per walk allowed is the third worst in baseball barely ahead of the Indians and Angels.
While those two teams are worse in that regard, both compensate somewhat with low home run rates. The Indians have allowed just 0.5 home runs per nine innings. The Angels are at almost exactly one home run per nine. By contrast, the Diamondback relievers have allowed over two home runs per game!
Arizona is well known for yielding home runs, but even adjusting the unit’s home run rate down with xFIP, they still post a 5.45 figure, which is half a run worse than what the 29th best unit, the Royals at 4.96 is. The Diamondbacks’ bullpen has the league’s worst ground ball rate.
According to tRA, the only reliever for Arizona that has managed to be above average is Carlos Rosa who has faced all of three batters. Of particular note for an atrocious level of play thus far are Bob Howry (8.96 FIP), Kevin Mulvey (14.09 FIP), Juan Gutierrez (7.32 FIP) and Esmerling Vasquez (6.71 FIP).