What to look for with a backhand shot to determine if it is leading edge or illegally played with the back of the stick.
The angle of the hook: if low to the ground it means a lot of the ‘back of the stick’ is exposed bit if the hook is slightly raised the ball will be played with the forehand edge of the stick
A spray of water before the ball is hit could mean they have hit the turf behind the ball causing the stick to lift over the ball so contact is with the back of the stick
A bouncy shot indicating a squeeze shot where the stick has come down on the top of the ball