Walked out from small wagon (6)
I believe the answer is:
struck
'walked out' is the definition.
('strike' can be a synonym of 'walk out')
'small wagon' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'wagon' becomes 'truck'.
's'+'truck'='STRUCK'
'from' acts as a link.
(Other definitions for struck that I've seen before include "Collided" , "Delivered a sharp blow" , "Hit, knocked with blow" , "'Hit, slapped (6)'" , "Found" .)