We have lots of cases - hockey being the best example but FAR from the only one - where players do things best described as shady and at worst fully described as criminally motivated.
I really think it is time that ALL sports add a clause to the contracts such that where there is evidence that a particularly vicious action that results in serious injury occurs, tapes will be reviewed. If there is even a HINT that the vicious hit was not accidental but rather was retaliatory, the player's case will be referred to the local prosecutor.
OK, in USA football, some of those tackles are not merely vicious, they are bone-crunching. Guys don't get up right away. Rare cases, they don't get up under their own power. One of the N'Awlins Saints players took one of those hits during the playoffs. In the post-game interview, one of the reporters asked him, "What was going through your mind after the hit." To which the player replied, "Remember to breathe!"
In hockey, you get knife-blades on your feet and a big stick in your hands. When a guy gets on the wrong side of either object there is usually blood on the ice. The sport is known to have "enforcers" who do exactly that sort of thing, and that just sucks.
Baseball and basketball have been known to clear the benches in brawls. In a few cases, objects get thrown - chairs and bats and such.
It should be made clear that any player so stupid as to jeopardize the career of another player for pride or revenge has NO PLACE as a professional athlete. Because when it gets to that level, it is not sports, it is the law of the jungle.
When the violence is used as an excuse to "level the playing field" - that's wrong. We pay money to SEE the good players trounce the bad ones. We don't want some hyperpituitary case leveling the good players so their mediocre team can win. That isn't sports. It is brute war.
On the other hand, everyone tells the ref to f... off, so it is hard to get riled up about it when it happens. It is when someone whacks the other player and when the ref gets in there to break it up, he whacks the ref just for good measure. That's crossing a line.
Just one man's opinion.