There may be no blocks below the waist on any play where there is a legal kick or after a change of possession.
Lining up for a try or a punt and not kicking the ball is different, foot must meet leather...
In close line play at the snap, linemen typically are blocking low trying to get leverage and that would not be a foul as in a vast majority of plays the contact initiates above the waist anyway. Like anything, sseeing the action would help a lot to determine if there was actually a foul
