Update: As per usual, RHM does a much better job with biographical information: apparently a big part of the reason that Mercker sat out the 2001 season is that he had a brain hemorrhage. Missed that. Yikes.
Mercker broke back in, with very limited success, as a reliever with the Rockies in 2002, but soon followed that with an outstanding year for the Reds and Braves in 2003. After another successful season with the Cubs in '04, Mercker resigned with the Reds for 2005 and became one of our few reliable relievers. The Reds are really counting on him for more of the same this year.
As always, additional biographical information on Mercker can be found in his profile in Red Hot Mama's Human League.
Historical Stats (for explanation of the stats used in this profile, please see the Baseball Statistics Quicksheet in the sidebar):
Typically, the Reds use Mercker as a late-inning set up man and occasional closer. As he ages and continues to decline, more and more of his value will be in the left-handed specialist role. He clearly can still be very effective in that role, but he should be watched closely--and probably replaced--against right-handers when the game is on the line.
The most troubling thing, however, has to be the PECOTA IP-projections, which show him dropping to between 34 and 40 IP this year compared to 50-60 IP the last three years. PECOTA bases its innings pitched projections (as well as all other stats) based on age-specific comparable players. That it predicts 34.3 innings pitched indicates that a number of Mercker's most comparable pitchers had substantially fewer innings pitched at age 38--most likely due to injury, but possibly due to ineffectiveness. We have already seen Mercker's back act up a little bit this season... I just hope he can beat the odds and stay healthy for us this year. If he does that, I look for him to continue to be our most reliable left-hander out of the pen.
Baseball Archive, The
Baseball Cube, The
Baseball Prospectus '06 Annual
Baseball Think Factory
Hardball Times '06 Annual