Originally Posted by the dmg
He's fared himself pretty well against walkers in the past, and was killing a few of them from the impact of the revolver in the last episode. He was also pinned against the the gate.I'd choke this up to him not physically and mentally breaking down. I mean, Herschel has stated that Rick hasn't gotten sleep since Lori died, he's most likely not eating or really keeping himself all that hydrated as well. His body is bound to get weaker.
He's a cop, so it stands to reason that he would also have some type of unarmed training. Your point about lack of proper nutrition and poor sleep is valid; I'm sure the entire group feels run down and weakened to various degrees. Yet it doesn't make sense to me that he freaked out against the gate instead of some police academy-honed sense of preservation taking over.