Run down motorway and get in a row (6)
I believe the answer is:
malign
'run down' is the definition.
(I've seen this before)
'motorway and get in a row' is the wordplay.
'motorway' becomes 'M' (as in motorway names - M1, M4 etc).
'and' is a charade indicator (letters next to each other).
'get in a row' becomes 'align' (I've seen this in another clue).
'm'+'align'='MALIGN'
(Other definitions for malign that I've seen before include "Laming, showing malice" , "Traduce" , "Evil-natured" , "Damaging - defame" , "Evil - slander" .)