Catch small badger (4)
I believe the answer is:
snag
'catch' is the definition.
(I know that snag is a type of catch)
'small badger' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'badger' becomes 'nag' (both can mean to annoy or complain at).
's'+'nag'='SNAG'
(Other definitions for snag that I've seen before include "hurdle?" , "Unforeseen obstacle" , "Complication, drawback" , "Jagged projection" , "A hidden or unexpected obstacle" .)