Work on place for the other side (10)
I believe the answer is:
opposition
'the other side' is the definition.
(opposing forces)
'work on place' is the wordplay.
'work' becomes 'op' (operation, work done in an operating theatre).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'place' becomes 'position' (synonyms).
'op'+'position'='OPPOSITION'
'for' acts as a link.
(Other definitions for opposition that I've seen before include "antagonism" , "Political party" , "parliamentary group" , "obstruction" , "Enemy" .)