Duck? Keen to catch duck (5)
I believe the answer is:
avoid
'duck' is the definition.
(duck can mean to avoid)
'duck? keen to catch' is the wordplay.
'duck?' becomes 'o' (resembles zero - 'duck' in cricket).
'keen' becomes 'avid' (both can mean enthusiastic).
'to catch' indicates putting letters inside.
'o' inserted inside 'avid' is 'AVOID'.
(Other definitions for avoid that I've seen before include "Stay clear of" , "Elude" , "Refrain from (something)" , "Stay away from or circumvent" , "Sidestep" .)