If you saw someone beating up another person, would you stop the attacker?

[benon]

If I thought I could stop it i would, but if I thought it was too dangerous to stop, I would call the police from a hidden place, and then hide my video camera somewhere, so that I might capture some evidence, handing over whatever I recorded to the police. I carry my camera everywhere, so it woudln't be hard to get my hands on it if I needed it.