Guerrilla in a strap after being injured (8)
I believe the answer is:
partisan
'guerrilla' is the definition.
(I know that guerrilla can be written as partisan)
'in a strap after being injured' is the wordplay.
'after' says to put letters next to each other.
'being injured' indicates an anagram.
'in'+'a'+'strap'='inastrap'
'inastrap' is an anagram of 'PARTISAN'.
(Other definitions for partisan that I've seen before include "Adherent" , "Devoted to a cause or party" , "Inclining to one side" , "Arts pain (anag.)" , "champion" .)