Taken literally - any sport where the goal is to injure the other. I believe the context here is mostly metaphorical - ie: don't engage in activities whose goal is to injure (physically or otherwise) another.
Historically that would have been animal fighting or hunting. It’s a euphemism for death rather than injury. Today some people interpret it more literally and include any sport where injury is expected. Which is to say, pugilism.
I read that and thought of zero-sum winner take all pursuits that are more performance than achievement. Office politics, trash talking in earnest, picking sides in conflicts that don't involve me, etc.
Sporting for the sake of blood, not for any kind gain. Metaphorical fox hunts if you will.