Means one against agrees to differ (8)
I believe the answer is:
averages
'means' is the definition.
(mean is a type of average)
'one against agrees to differ' is the wordplay.
'one' becomes 'a'.
'against' becomes 'v' (abbreviation for 'versus').
'to differ' indicates an anagram.
'agrees' is an anagram of 'erages'.
'a'+'v'+'erages'='AVERAGES'
(Other definitions for averages that I've seen before include "Data included in cricket statistics" , "Evens out to" , "estimations of mean" , "Save rage (anag.)" , "that are of great concern to cricketers" .)