Citizens arrest.

Is it legal for citizens to arrest people they see breaking the law ?

If someone is assaulting someone can you detain them or do you have to be an actual officer of the law ?

If you see a bunch of guys in masks driving cruising the streets can you arrest them for refusing to show proof of citizenship?

If a bunch of dudes all jump out of a car and leave it blocking the road is it legal to detain them for dangerous driving ?

If you see someone grab someone and throw them on the street for not having ID can you grab them and throw them on the street for not having ID ?