Grass over lovely Cambridge Backs (3)
I believe the answer is:
rye
'grass' is the definition.
(I've seen this before)
'over lovely cambridge backs' is the wordplay.
'backs' indicates one should take the final letters (I've seen 'back' mean this).
The last letters of 'over lovely cambridge' are 'RYE'.
(Other definitions for rye that I've seen before include "Grass - whiskey" , "Whisky; Sussex town" , "Kind of serial or American whiskey" , "Wheat-like cereal plant" , "Gypsy gentleman" .)