Limit beer in grounds (9)
I believe the answer is:
rationale
'grounds' is the definition.
(I've seen this in another clue)
'limit beer' is the wordplay.
'limit' becomes 'ration' (rationing is a kind of limiting).
'beer' becomes 'ale' (type of beer).
'ration'+'ale'='RATIONALE'
'in' acts as a link.
(Other definitions for rationale that I've seen before include "Philosophy" , "grounds?" , "Reasoned exposition" , "Logical reasons (for action)" , "Logical basis (for a course of action)" .)