How would u handle urself, overkill or mercifull?

[JohnnyS]

You're required by law to only use as much force as necessary. That may seem vague, but if you knock someone down then stomp on their head you can get charged with "assault with a deadly weapon", if not worse. In the eyes of the law, kicking someone when they're down is just as bad as stabbing them. So be careful.

 

You should end the fight, not seek to punish the guy and deliberately put them in hospital.