A particular team - leader in division - is biased (3-5)
I believe the answer is:
one-sided
'biased' is the definition.
(I know that biased can be written as one-sided)
'a particular team leader in division' is the wordplay.
'a particular' becomes 'one'.
'team' becomes 'side' (both can mean a sports team).
'leader in' says to take the initial letters.
The first letter of 'division' is 'd'.
'one'+'side'+'d'='ONE-SIDED'
'is' acts as a link.
(Other definitions for one-sided that I've seen before include "Unfair or partisan - single dimension?" , "Partial" , "Grossly unequal; biased" , "Unequal like contest between badly matched opponents" , "Unfair, unequal" .)