Jog and play boisterously in gym (6)
I believe the answer is:
prompt
'jog' is the definition.
'play boisterously in gym' is the wordplay.
'play boisterously' becomes 'romp' (I've seen this before).
'in' means one lot of letters goes inside another.
'gym' becomes 'PT' (Physical Training).
'romp' going within 'pt' is 'PROMPT'.
'and' acts as a link.
(Other definitions for prompt that I've seen before include "Whisper line to forgetful actor" , "Whisper lines to forgetful actor" , "Cause; on time" , "Punctual or timely" , "Bang on" .)