Beats leg side with a 90-degree turn? (7)
I believe the answer is:
topspin
'with a 90-degree turn?' is the definition.
(as in a ball with topspin)
'beats leg' is the wordplay.
'beats' becomes 'tops' (both can mean to outdo or better).
'leg' becomes 'pin' (pin is a kind of leg).
'tops'+'pin'='TOPSPIN'
'side' is the link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for topspin that I've seen before include "What can make a ball curve" , "Curving ball's rotation" , "Warne might use this" , "Feature of bowling" , "What bowler might impart to a ball" .)