Exercise in estate, perhaps, as a prank (5)
I believe the answer is:
caper
'a prank' is the definition.
(I know that prank can be written as caper)
'exercise in estate perhaps' is the wordplay.
'exercise' becomes 'pe' (Physical Education).
'in' means one lot of letters goes inside another.
'estate perhaps' becomes 'car' (estate is a type of car).
'pe' going within 'car' is 'CAPER'.
'as' acts as a link.
(Other definitions for caper that I've seen before include "prickly shrub" , "Ridiculous escapade" , "High-spirited escapade" , "Lark" , "Antic, prank" .)