Antagonism, for some strange reason (5)
I believe the answer is:
anger
'antagonism' is the definition.
(thesaurus)
'some strange reason' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ANGER' is hidden in the letters of 'strange reason'.
'for' is the link.
(Other definitions for anger that I've seen before include "exasperation" , "There's fury" , "Hack off" , "Strong feeling of annoyance" , "Strong displeasure" .)