Bother over sauce (5)
I believe the answer is:
pesto
'sauce' is the definition.
(I've seen this before)
'bother over' is the wordplay.
'bother' becomes 'pest'.
'over' becomes 'o' (cricket abbreviation).
'pest'+'o'='PESTO'
(Other definitions for pesto that I've seen before include "Italian sauce containing basil" , "Basil-based sauce" , "Ligurian food" , "Sauce made of basil and cheese" , "sauce involving Basil" .)