SteveA's post is a strong one and cites some case law. But "implied consent" is usually a factor in sporting cases. Boxing, for example, superficially would be appear totally illegal except that anyone getting into the ring is deemed to have consented to being punched by the opponent. In comparison with SteveA's case it could be said that punching is within the laws of boxing but I think some punches (e.g. after the ref has said "break", or "rabbit punching" the kidneys} are outside the rules but I don't remember anyone being taken to court for any of them. In football, several forms of tackle are ruled illegitimate but may not be illegal. Mostly however, I suspect that police and prosecutors are diffident about making interpretations about the legalities of contacts in what are clearly "contact sports" unless given firm guidance by the ruling bodies of those sports. Most sporting ruling bodies don't want to do that.