If you see police brutality being committed, is it within your rights to make a citizen’s arrest?

I would like to think if I saw Rodney King: The Sequel taking place, I could do something to stop it, but unsure of the legal implications. Any advice on this?
To restate the question: if I see any act of what could be reasonably considered unconscionable and gratuitous violence towards a citizen by a police officer, is it then just cause for me to make a citizen’s arrest in order to bring the violence to a stop?

You are not equipped to arrest police and will only get hurt. You should consult an attorney before taking any steps to do what is right. Your life will be placed under a microscope and could be turned upside down. BUT if you have seen an injustice and are in a position to do something (as advised by an attorney), then it may well be worth it. Most likely those officers will do it again. It could be you, your family, your friend, or anyone…next time.