He ran because he had just attacked Rick with an axe and Rick was about to retaliate.
The bearded guy, didn't catch his name, claimed he was a nonviolent prisoner-- but did anyone notice how many times, and how fiercely, he shanked that zombie in the gut during their "run amok" attack?
I got a good laugh out of how they ignored Every. Single. Thing. Rick's group told them ("We know how to kill a man!"), and Rick's group just stood by watching them, rolling their eyes.