Note bodyguard having a rest (9)
I believe the answer is:
remainder
'rest' is the definition.
(I know that rest can be written as remainder)
'note bodyguard having a' is the wordplay.
'note' becomes 're' (as in do-re-mi).
'bodyguard' becomes 'minder' (I've seen this before).
'having' is an insertion indicator.
'minder' placed around 'a' is 'mainder'.
're'+'mainder'='REMAINDER'
(Other definitions for remainder that I've seen before include "The part that is left over" , "It's left over after division" , "butt" , "that's left" , "Balance" .)