Could you get in trouble if you defend someone from attack?

Generally speaking, you are only allowed to use reasonable force to defend yourself from imminent harmful or offensive physical contact or unless such contact has already occurred. Mere words (threats, insults, etc.) are never enough without some overt action that can reasonably show you were coming into harm.

This principle also applies in the defense of others. As long as the person being attacked has the right to use force to defend himself, you can generally use reasonable force to defend him.

In your hypothetical, unless you were willing to get hurt yourself, your best bet is to call the cops and hide. The dispatcher would be the first person to tell you to stay out of the way.

They can always sue. You have a defense.

The sad truth is, you can always get in trouble for anything or nothing at all. All it takes is the right situation, or a bully cop who thinks you need to be taught a lesson. "Innocent until proven guilty" is a myth. In the real world we all know your guilty, we just have to prove it.

The police are going to assume that your also a gang member. They'll arrest you and question you. If your lucky the police will believe your story. But don't count on it, and don't count on anyone really caring if your guilty or innocent or if you had good intentions. They just care about putting people in jail.

Yes, they can sue you. And then you have to hire a lawyer and prove in court that what you did was necessary.

Example. If after the guy is down, you keep hitting him (even one time) and then it becomes assault. You could end up paying his medical expenses. But usually gang members don't sue.

I can't tell you what you should do. But... When I took life guard training, one important thing we learned is to NOT just jump in. Jumping into the water to save someone is dangerous. All kinds of things can happen. The better option is to look around and see if you can throw something to the victim, or can you reach the victim without jumping in. Too often people just react without knowing and they make the situation worse.

So before you jump into a fight, you should look for a better option. Maybe if you just yelled at them, that might scare them off.