Score one less (8)
I believe the answer is:
nineteen
'less' is the definition.
The answer and definition can be both quantities as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'score one' is the wordplay.
I cannot really understand how this works, but
'score' could be 'net' (both can mean to obtain or secure) and 'net' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for nineteen that I've seen before include "Roman XIX" , "12 + 7" , "after the round, the number for the next round?" , "Prime number" , "not quite the full score" .)