I've never actually had a friend get shot in front of me before, but I've been airsofting before, and generally, when I see anybody get "shot" the first thing I do is duck down and look around for where the shot came from, or try to get behind something.
Really? Airsofting? Okay, first of all, you know what's going down - it's not even "many things could happen, being shot one of them" - in airsoft it is almost 100% - someone going to get shot. So to not expect someone getting shot would be dumb. Talking with a mate in a hideout as a bandit would be reasonably more taken aback by an arrow just coming from nowhere and impaling his head.
Just such a dumb reasoning! And also, of course your response is going to be - okay, so and so is down (like hit with paintballs or the like), a bit different than seeing a friend injured or killed in front of you. Argh...