Contests work against models (7)
I believe the answer is:
opposes
'contests' is the definition.
(to contest something is to oppose or object to it)
'work against models' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'against' says to put letters next to each other.
'models' becomes 'poses' ('pose' can be a synonym of 'model').
'op'+'poses'='OPPOSES'
(Other definitions for opposes that I've seen before include "Strongly disapproves" , "Stands against" , "Disagrees with and attempts to prevent" , "Counters" , "Goes against" .)