Posed outside back of shop in row (4)
I believe the answer is:
spat
'row' is the definition.
(spat is a kind of row)
'posed outside back of shop' is the wordplay.
'posed' becomes 'sat' ('sit' can be a synonym of 'pose').
'outside' is an insertion indicator.
'back of' indicates one should take the final letters.
The final letter of 'shop' is 'p'.
'sat' enclosing 'p' is 'SPAT'.
'in' acts as a link.
(Other definitions for spat that I've seen before include "Reacted contemptuously" , "Expelled" , "Pat's involved in petty quarrel" , "Expectorated in slight quarrel" , "Disagreement" .)