Blindly loyal to one side (8)
I believe the answer is:
partisan
'blindly loyal to one side' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for partisan that I've seen before include "Prejudiced towards one cause" , "Enthusiastic supporter" , "Devotee of a cause" , "Strongly supporting one side" , "Unquestioning supporter -- aspirant (anag)" .)