Don't let others say bad things about your friend, either. Until you've had a chance to hear your friend's side of the story, treat comments that are not supportive as hearsay and rumors. If someone says something that shocks you and doesn't seem like a thing your friend would do or say, then respond with something like, "I know him/her, and that just doesn't sound right. Let me talk to him/her, find out his/her perspective on this. Until then, I would appreciate it if you didn't spread that around.