Be going over right lines for fruit (5)
I believe the answer is:
berry
'for fruit' is the definition.
(berry is a kind of fruit)
'be going over right lines' is the wordplay.
'going over' says to put letters next to each other.
'right' becomes 'r' (abbreviation).
'lines' becomes 'ry' (abbreviation for railway).
'be'+'r'+'ry'='BERRY'
(Other definitions for berry that I've seen before include "Small round stoneless fruit, may be black (5)" , "Small juicy fruit" , "'One might be straw, rasp or blue, say (5)'" , "Romeo's family" , "Small edible fruit" .)