Joke that's on jerk (3-4)
I believe the answer is:
leg-pull
'joke' is the definition.
(I know that leg-pull is a type of joke)
'on jerk' is the wordplay.
'on' becomes 'leg' (cricket term).
'jerk' becomes 'pull' (I've seen this before).
'leg'+'pull'='LEG-PULL'
'that's' acts as a link.
(Other definitions for leg-pull that I've seen before include "Good-humoured hoax" , "Trick; practical joke" , "Informal hoax involving lower limb" , "Jolly jape involving lower limb" , "Hoax exerted on lower limb?" .)