Cowser is not good against left-handed breaking balls. He wasn't in the minors, and he's not going to be against them in the majors any time soon.
There was no doubt he was sitting dead red on the 0-0 for some reason.
Obviously no one wants Cowser up in that situation against that pitcher, but the way the bench was set up, only O'Hearn and Kemp were in the game and things start getting dicey defensively if O'Hearn has to come in for Cowser if the game ends up tied going into the 10th. Then again, O'Hearn is not exactly known for hitting left-handers either.
This might be a good reason to have had Nevin instead of Kemp on the final roster. Have we found a reason why Kemp is on this roster besides keeping Holliday down until they gain the extra year of control?