Flagged down (6)
I believe the answer is:
hailed
'flagged down' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for hailed that I've seen before include "Greeted or sginalled to" , "Greeted or saluted" , "Called, a cab say" , "Greeted (with ice pellets?)" , "Greeted like ancient Romans" .)