Jun Morimoto brings up an interesting thread on violence in sports and why we allow sports to sidestep civil and criminal law. It's related to the increasingly contentious conflict between sports league rules and employee and human rights. His stance is basically that as the participants freely signed up to play, they have accepted the risk of violence, though to a greater or lesser degree depending on the sport. I agree on his distinction between what you freely signed up for and could reasonably expect, and what you did not. When you start boxing or judo, you agree to get beaten up as part of the game. Jun brings up tattoos and body piercings as another kind of activity that, since it is completely voluntary, is not criminal.
But the "implicit consent" of violence beyond that which is expected is just that - implicit, and quite possibly non-enforceable would it come to that. When Zidane headbutted Materazzi in a soccer game, that went beyond implicit consent. Mazeratti did very much not sign up for the possibility of a headbutt (a move that can potentially kill the victim if it hits badly) when agreeing to participate in the match. If, just to take a pure hypothetical, he had chosen to sue Zidane over it, it is not at all clear that the suit would be dismissed. And I, at least, don't think it should be.
There are other areas with a large "don't go there" legal gray zone; the largest is probably religion. Many societies give religious organizations a de-facto jurisdiction over their congregations, including children (that can't reasonably have said to have given free, informed consent). On one end you have a recent case in the US where a 17 year old girl was held captive against her will for two days and beaten up as part of an involuntary exorcism. The court ruled that it had no standing to try the case since in their view it would collide with the separation of church and state.
Overall, though, the trend seems to go the other way, with civil society claiming pre-eminence over special interests. There is a fair amount of debate about gay marriage in many countries, for instance, with proponents and opponents in heated debate. But that is really just a consequence of an earlier, far more fundamental shift of marriage from a primarily religious institution to a primarily civil one. In many countries you can get married today without asking a church for permission; indeed without having any religious input at all. You can also get named, be considered an adult, own property and be buried - all without involving religious authorities or asking them for permission.
This was not always the case (and still isn't in some parts of the world). In the not so distant European past, the various christian churches wielded political and secular power at least equal to - and frequently greater than - the secular rulers. With the continuing rise of civil society (including the rise of the national state) as the dominant force, the religious rulers have lost much of their power - and lost it quietly, unnoticeably through the emergence of legal rules for areas once religious. Once there is a law or rule regulating something, civil society has taken ownership of and responsibility for it.
In the same way, the recent conflicts between the sporting world and civil society is, I think, a reflection on the latter's increasing dominance. I believe this is mostly a good thing. It does not mean that religions or sports leagues should never be allowed exceptions to regular laws, but it does mean that any exceptions be made explicit and transparent, rather than remain enacted by default.