Difficult billiards shot reveals the fool in me (5)
I believe the answer is:
masse
'difficult billiards shot' is the definition.
(I've seen this in another clue)
'the fool in me' is the wordplay.
'the fool' becomes 'ass' (both can mean a stupid person).
'in' indicates putting letters inside.
'ass' going within 'me' is 'MASSE'.
'reveals' is the link.
(Other definitions for masse that I've seen before include "'En ..., all together (5)'" , "Swerve shot at billiards" , "Swerving snooker stroke" .)