If I poke at someone on the street with a metal stick, I would rightly be arrested for assault. If I perform the same action on a fencing strip, people applaud. Does that not put the venue beyond the law?

Likewise, tackling people is considered assault unless it occurs on a football field.

Now, if I punch somebody in either of those locations, it is a foul, punishable within the rules. Anything beyond that would probably be prosecuted.

Context is applicable in the definition of what constitutes violence. Those who participate in the sports are probably best suited to determine what is violence and what is within the rules.