Excessive force on behalf of the bouncers, and idiocy on behalf of the drunks who initiated with aggressive posturing and continued to approach after it was obvious they were outmatched.
The first bouncer kicks his downed opponent in the groin after he falls. The second slaps him down again when he gets up and refuses to leave. A friend attempts to intervene and is punched.
Victim stepped into striking range without watching opponent, did not appear to understand the risk and how fast the situation can change. This was potentially fatal due to the hard surface.
Key mistake is that the police officer fails to keep a safe distance or at least adopt a defensive posture and bladed stance while close to the suspect. Incident appears to be mental health related.
Victim standing with hands in pockets within striking range. Aggressor does not telegraph, strikes while talking to distract victim. Striking from this range happens so quickly that it is impossible to react in time for the vast majority of people.
A potentially fatal slam. High risk of severe head injury.