Bird catcher's practical joke (5,4)
I believe the answer is:
booby trap
'practical joke' is the definition.
(I've seen this before)
'bird catcher's' is the wordplay.
'bird' becomes 'booby' (booby is a kind of bird).
'catcher' becomes 'trap' (I've seen this in another clue).
'booby'+'trap'='BOOBY-TRAP'
(Other definitions for booby trap that I've seen before include "mine?" , "Lethal or playful device set off by victim" , "Device for practical joke" , "Bra, maybe" , "Hidden weapon" .)