Bit of tomfoolery (5)
I believe the answer is:
antic
'bit of tomfoolery' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for antic that I've seen before include "Playful caper" , "Mad act done for fun" , "old buffoon" , "Absurd action" , "Eccentric once" .)