Lettuce bag for Russian cavalryman? (7)
I believe the answer is:
cossack
'russian cavalryman?' is the definition.
(I've seen this before)
'lettuce bag' is the wordplay.
'lettuce' becomes 'cos' (cos lettuce is a kind of lettuce).
'bag' becomes 'sack' (both can mean a container).
'cos'+'sack'='COSSACK'
'for' acts as a link.
(Other definitions for cossack that I've seen before include "Russian tribesman famed for horsemanship" , "One of a people from SW Russia, Ukraine" , "Member of an elite cavalry in tzarist Russia" , "Warrior peasant of SE Russia" , "Russian, traditionally horseman of the Steppes" .)