Quarrel seen in bar (4)
I believe the answer is:
bolt
This clue is a double definition.
'quarrel' is the first definition.
(thesaurus)
'bar' is the second definition.
(bolt is a kind of bar)
'seen in' acts as a link.
(Other definitions for bolt that I've seen before include "Run away; bar of lock" , "Flee with door-locking device" , "Flash of lightening - run away" , "Leave suddenly and in a hurry" , "Leg it < and consume apace" .)