Fowl's leg better tucked behind (5)
I believe the answer is:
capon
'fowl's' is the definition.
(capon is a kind of fowl)
'leg better tucked behind' is the wordplay.
I cannot really understand how this works, but
'leg' could be 'on' (cricket term, fielding positions) and 'on' is found in the answer.
'better' could be 'cap' (both can mean to beat somebody else's attempt) and 'cap' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for capon that I've seen before include "Emasculated fowl" , "Castrated cock fowl" , "Male chicken for eating" , "Castrated fowl, for eating" , "Castrated bird" .)