Expelled for minor disagreement (4)
I believe the answer is:
spat
This clue is a double definition.
'expelled' is the first definition.
(I've seen this before)
'minor disagreement' is the second definition.
'for' is the link.
(Other definitions for spat that I've seen before include "Contretemps" , "Taps in minor quarrel" , "A minor dispute or row" , "Pat's involved in squabble" , "Minor difference" .)