The zombies had accurate ranged attacks that were kicking our asses, and they weren't coming out of the water, so the Paladin waded in to challenge them and draw their fire from our softer targets. It may not have been the most tactically sound option, but that's what that particular player is like (he also got us caught in a goblin deadfall trap that nearly got us all killed, but that's another story entirely).
In that case though, I think the fighter should have backed up his fellow defender, especially after a few rounds went by and it was obvious that our squishies weren't going to be ambushed from behind.
We all roasted him about it afterward, singing the "Brave Sir Robin" song from Holy Grail, but inserting his character's name and deeds into it.