mid-field crosswind
This should have been banned long ago. Mainly because everyone seems to have such a different interpretation of what it actually is and the way it is implemented.
Joining crosswind over the threshold appears on the surface to be far safer, as your only risk is a high-performance aircraft on takeoff (who can likely clearly see you ahead) and for the aircraft joining crosswind, his only real concern is an aircraft on downwind or joining downwind.