Then you can charge/sue them for unnecessary force.
excessive use of force
Your question is worded ambiguously. Is the "they" in your question the police officers, or the people who are the victims of the excessive force?
no
You are probably looking for a Section 1983 claim.
It would be 'illegal' if they had no articulable reason to touch you in the first place. It could be 'excessive' if they did have reason to lay hands on you, but did so in an excessive manner and/or continued to use force on you after you had been subdued and restrained.
Excessive Force was created in 1991.
Excessive Force was released on 05/14/1993.
The Production Budget for Excessive Force was $13,000,000.
Excessive Force grossed $1,152,117 worldwide.
Excessive Force grossed $1,152,117 in the domestic market.
No, you can't. The best action may be for everyone to calm down and stop struggling. If you jump into the fray while an excited police officer is trying to subdue a suspect then you will be charged and possibly injured. Unfortunately, some police officers do use excessive force. People in some areas need to modify their behavior so as not to attract police attention by being intoxicated in public, violating traffic laws, not engaging in combat or domestic disputes with others, and not interfering when the police are trying to quell a disturbance.
The beating of Rodney King by police officers in 1991 was a result of excessive force during a traffic stop. The incident was caught on video, sparking outrage and leading to national debates on police brutality and racial injustice.