Oddly, archers are cards (4)
I believe the answer is:
aces
'are cards' is the definition.
(I have seen 'Top cards' mean 'aces' so perhaps 'cards' could also mean 'aces')
'oddly archers' is the wordplay.
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
The alternating letters of 'archers' are 'ACES'.
(Other definitions for aces that I've seen before include "Honours" , "that are non-returnable" , "passes with flying colours in US" , "wartime pilots?" , "Top cards or people" .)