I'm big on precision. I probably already got nitpicky when I talked about "prescriptions" for weed today. They don't exist, recommendations do.
When I think of something shady, it's usually something I wouldn't do. Legality doesn't necessarily come into play, unless legality coincides with my interpretation of morality. Personally, I think huge weight-cuts are shady, particularly when fighting a much smaller opponent. But they're legal.
Would I knee check someone that was scoring low kicks? In a heartbeat.
Would you call Gonzaga headkicking CroCop out shady? It effectively ended his career.