In general, dealing with a patient in an altered state:
Stand alongside them, not in front of them.
Steer them towards a place of relative calm and quiet.
Establish neutral, concerned touch only, such as lightly touching the elbow.
Ask questions; this establishes you as a concerned outsider, something new to the situation not a part of it, and it encourages dialogue.
Be sincere - make your own goal to help this person even if they are in fact the problem. Confrontation triggers confrontation. Concern triggers trust.
All that aside, never ever forget for a moment that people in altered states, even when seemingly frail, are very dangerous and prone to sudden changes in thought and behavior.
Also never underestimate the dangers of group psychology. A single drunk is easily managed, but groups feed off each other's emotions and escalate quickly.
Dealing with a group: have a larger group. Seriously. Barring that, establish yourself as a friendly outsider, show no fear, smile and project sympathy and humor, stay outside the group boundary, reconsider the wisdom of what you're doing.
Call 911. Consider if you really want to enter a crowd (5-1 can be quite a crowd if you're getting beaten) ... if the situation is stable enough for there to be time for police and medical help to arrive, doing nothing but alerting them may be the best thing to do rather than trigger some unexpected change in the situation.
I suppose if someone were in danger of death,+ I would enter the situation ... If so I would approach saying "hey she needs medical help, I am going to give her help to breathe, she needs help breathing, I'm giving medical help, hey guys what happened to her she's pretty sick huh?"
Bear in mind as a lone individual you might exude the calm of a saint and still find yourself in peril or making the situation worse - an individual cop has a weapon, authority, and a shitload of backup when stepping in and this has a deterrent effect on most people, but even a cop is going to want to get backup rolling before diving into whatever craziness you witnessed.
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