From behind, hold down and grind vegetable (6)
I believe the answer is:
turnip
'vegetable' is the definition.
(turnip is a kind of vegetable)
'from behind hold down and grind' is the wordplay.
'from behind' says the letters should be written backwards.
'hold down' becomes 'pin' (as in pinning down).
'and' says to put letters next to each other.
'grind' becomes 'rut' (both can mean a repetitive routine).
'pin'+'rut'='pinrut'
'pinrut' in reverse letter order is 'TURNIP'.
(Other definitions for turnip that I've seen before include "Fleshy edible white or yellow root" , "Plant with round white root used as vegetable" , "food item" , "veggie" , "what you eat?" .)