What you can see in bars, turning up for attack (3,2)
I believe the answer is:
set on
'attack' is the definition.
(I know that attack can be written as set on)
'what you can see in bars turning up' is the wordplay.
'what you can see in bars' becomes 'notes' (musical notes in bars of music).
'turning up' says the letters should be written in reverse.
'notes' written backwards gives 'SET ON'.
'for' acts as a link.
(Other definitions for set on that I've seen before include "Determined" , "Go" , "Attack" .)