I already looked at the 20 best, as measured by WPA,so it only seems appropriate to look at the 20 worst. I'll be using WPA again, but it's by no means the only metric you could use to create a similar list. I'll be doing so without any commentary this time and will be breaking it down into pitchers and position players because late-inning relievers are easily going to have had the most negative impact on the game (think Carlos Marmol blowing a 32 run lead by walking 36 straight).
Of course Koyie Hill would be in this list. I'm actually surprised Joe Mather isn't in it more frequently. Soriano and Castro each made the list 3 times, but when you play as many games as those two did, that's going to happen. Not surprisingly, the Cubs closer led the way with 4 times on the list. That's probably true of almost every team.