There's always been a bit of a debate of where the law starts and finishes in a sporting arena. It's a while ago now but i seem to remember something in football many years ago, 1 was to do with Duncan Ferguson and the other Gary Mabbutt and "Fash the bash".
Thankfully I can't recall anything similar in Speedway, I suppose the equivalent in Speedway would be somebody with a reputation like Nicki Pedersen going too far and "fencing" an opponent with the worst possible outcome. Then it's a matter of opinion of whether it was a deliberate action or not.
Fortunately, as far as I'm aware, the sport has never had to deal with this, but it came very close this summer with the Craig Cook incident.