Acting foolishly on the golf course? (7,6)
I believe the answer is:
playing around
'course?' is the definition.
I know nothing about this answer so I can't judge whether this works.
'acting foolishly on the golf' is the wordplay.
'acting' becomes 'playing' ('play' can be a synonym of 'act').
'foolishly on' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'the golf' becomes 'round' (round is a kind of golf).
'playing'+'a'+'round'='PLAYING AROUND'
Can you help me to learn more?
(Another definition for playing around that I've seen is " Seeing someone".)