Sorry just had to reply to this, long time viewer, new to posting.
As a referee and someone within the Police service I felt I had to clear this up. In its simple terms, violent conduct on the field of play does break British law, and as such, any form of it could be (and should be in my book) reported to the Police. Its simply some sort of unwritten rule that getting whacked at football is acceptable. I have below linked the very definition from the PNLD (Police National Legal Database), which shows anything that happens outside of the sporting rules is not covered by the LOTG. What it means is, you give consent that you may suffer a accidental clash of heads etc...not getting punched in the face. It happened in a game I was involved in last season, where by player A said something to player B, player B head butted him, causing quite a nasty injury, and was sent off for violent conduct, it was reported to the police and player B was found guilty of ABH, and rightly so. Plus Self defence doesn't give you right to retaliation, it is there to defend yourself. Just felt the need to clear this up as it seems to have caused a bit of a stir, and hopefully going forward, officials will know that if they think something needs to be done outside of football then it can be, the only way to get violence out of the game we all love is if its dealt with properly. Some times a 35 day ban and £70 fine is nothing to these people, 180 community service, £600 fine and a criminal record just might.
Lawful sports
This defence covers participation in all lawful sports which might result in injury due to their very nature, including boxing (under the Queensberry rules), soccer, rugby etc. Properly conducted sports are considered to be for the public good and therefore any assaults and batteries which take place during the course of the contest within the rules are lawful and the opposing players are taken to have given their consent to the injuries which they might suffer during the course of the match or contest. Such consent is even to the risk of potentially fatal injuries. Any injury caused by a player acting outside the rules of the sport will be an assault, and criminal proceedings should be considered.