One retaining a clean sheet? (6)
I believe the answer is:
keeper
'one retaining' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'a clean sheet?' is the wordplay.
I cannot really see how this works, but
'a' could be 'per' (eg 'one a day' means 'one per day') and 'per' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for keeper that I've seen before include "SECOND PART OF 16" , "Goal minder" , "Goalie" , "Zoo worker" , "Football or cricket player" .)