Check rule, having lost golf (4)
I believe the answer is:
rein
'check' is the definition.
(both can mean to control or limit)
'rule having lost golf' is the wordplay.
'rule' becomes 'reign' (reigning is a kind of ruling).
'having lost' indicates named letters should be taken away.
'golf' becomes 'g' (phonetic alphabet: alpha, bravo, charlie etc.).
'reign' with 'g' taken away is 'REIN'.
(Other definitions for rein that I've seen before include "Hold back" , "Free ... is carte blanche" , "Restraint; strap attached to horse's bit" , "Long strap to restrain" , "Leather used for control in horse-riding" .)