Attack the piece and get an unfair advantage (4,3,3)
I believe the answer is:
jump the gun
'get an unfair advantage' is the definition.
'attack the piece' is the wordplay.
'attack' becomes 'jump' (jumping is a kind of attacking).
'piece' becomes 'gun' (I've seen this before**).
'jump'+'the'+'gun'='JUMP THE GUN'
'and' acts as a link.
(Other definitions for jump the gun that I've seen before include "Be too hasty" , "Start too quickly" , "Leave too early" , "Start too early" , "Come too early out of the starting blocks?" .)