Horseman in company with small bag (7)
I believe the answer is:
cossack
'horseman' is the definition.
(I've seen this before)
'company with small bag' is the wordplay.
'company' becomes 'co' (abbreviation).
'with' means one lot of letters go next to another.
'small' becomes 's' (abbreviation - e.g. clothes size).
'bag' becomes 'sack' (both can mean a container).
'co'+'s'+'sack'='COSSACK'
'in' is the link.
(Other definitions for cossack that I've seen before include "Tsarist cavalryman" , "Russian or Ukrainian cavalryman" , "Russian tribesman famed for horsemanship" , "Member of Russian, Ukrainian people" , "Warrior peasant of SE Russia" .)