It depends on the circumstances. I had a client who had been roughed up by some rugby players and he was prosecuted for assault. It turned out that the rugby players had detained him while the Police arrived. My client had attacked a perfectly respectable family who were celebrating their son going to university. They were attacked because they had helped an asian family who were having car trouble and my client and his mates didnt like asians. The mans wife was headbutted and had a broken nose and teeth knocked out. His son was physically thrown through the car window and the father was kicked to the face while on the floor.
The rugby players interevened and held on to these thugs until the police arrived. My client was most indignant that he had been charged after being roughed up. They were all sent to prison and I decided I would rather prosecute criminals than defend them in future.
Like I said it all depends on the circumstances