Tris isn't bleeding. She's not sure what shot her. Maybe this is just an impromptu game of paintball? Do those actually happen?
Some people did die, and Tris takes a Dauntless armband from a body so that she can blend in.
Uriah shows up and encourages Tris to run, but she wants to find out what's going on first. She heads to the second floor to look for the Divergent.
Sure enough, they're rounding up the Divergent like cattle. Tris manages to help a little girl run away, but she gets caught by Eric, the guy whose defining characteristic is that he's totally evil.
Tris almost escapes from Eric by using her patented foot-stomping move (surely learned from watching Miss Congenialitytwo hundred times), but Eric overpowers her.
Tris is not afraid, even though she has a gun pressed to her head. She has a knife in her pocket.