Chaps score in terms of intellect (8)
I believe the answer is:
mentally
'in terms of intellect' is the definition.
'chaps score' is the wordplay.
'chaps' becomes 'men' (I've seen this before).
'score' becomes 'tally' (tally is a kind of score).
'men'+'tally'='MENTALLY'
(Other definitions for mentally that I've seen before include "by way of intellect" , "Using the mind" , "not physically" , "in the head" , "rationally" .)