Perfect hit to leg (4,2)
I believe the answer is:
bang on
'perfect' is the definition.
('bang on' can mean exactly right)
'hit to leg' is the wordplay.
'hit' becomes 'bang' (synonyms).
'to leg' becomes 'on' (cricket term, fielding positions).
'bang'+'on'='BANG ON'
(Other definitions for bang on that I've seen before include "Keep talking tediously" , "Exactly right; talk tediously (about)" , "Informally and absolutely accurate; it's explosive" , "Talk at length" , "Absolutely right, informally explosive" .)