There are classes like
$1, and most general self-defence courses can be adapted for the blind, with a qualified instructor. However, it isn't likely that a homeless man has received any of this training. Neither have I, for that matter. But the one time it seemed pretty likely I was going to get a beating, random strangers in the area stepped in to help me out. I suspect people are more likely to step in if they see an obviously blind man in trouble. So that might work to his advantage, if he stays in crowded areas.