In the U.S. essentially any person can sue any other person for any reason. You only win if you convince the judge or jury that you are right and the other person is wrong.
Yea
go to the cops and tell them.
No. the cops has to know who's been attacked.
Assault and vandalism.
Anyone can sue anybody for anything, but you're going to have a difficult time of it if they actually observed the assault taking place or were acting on the complaint of the person you allegedly assaulted.
It's assault so yeah. you could
By law, the cops are not allowed to force you to sue if someone breaks your nose. They won't say:"You won't sue him/her for breaking your nose, you're going to jail." They're not allowed to do that. You're the victim, so you decide wether you sue or not. If you refuse to sue or file a police report, the cops will respect that, but they will tell you the consequences of not suing or filing a police report or taking your assailant to court.
call the cops. That's assault brotha.
If you slapped your girlfriend you might be charged with assault or domestic violence.
In most of the world, no, but you can press charges for assault. In the USA, you can probably sue them for anything you like.
yes
Not usually. Although you can file criminal charges for assault.