MattyP - I can't give you exact examples but I do recall cases in the past (few and far between) of offenders being taken to court, but I cannot be sure if any were jailed.
In my time as Society Chairman (7 years) we have had four cases of police involvement with alleged assault - two involved referee red card dismissals, and two unseen off-the-ball incidents (one cited by the assessor, the other by the victim's club).
Witness statements taken, incuding the referee, lots of admin and meetings with clubs, County RFU management and disciplinary committees and in three cases the RFU Disciplinary Manager too.
One case went no further than a police warning, in two cases the police were advised by the CPS to not prosecute, and in one it did go to court and a non-custodial sentance awarded. In all four cases, after police involvement was completed, the usual CB Discpline Hearings took place and various bans were imposed.
Based on my experiences of these four cases, and others which have had no police involvement, the overall sentiment is that such thuggery has no place on the rugby pitch. Also the common argument of self-defence is in reality not sustainable when an injury is caused. Time after time I have seen "changing-room" lawyers and defendants pleading not guilty, who argue the self defence line, or provocation & retaliation argument, be taken to pieces by the Disciplinary Committee and found guilty.