Almost performing murder (2,2)
I believe the answer is:
do in
'murder' is the definition.
('do in' can mean to kill)
'almost performing' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'performing' becomes 'doing' ('do' can be a synonym of 'perform').
'doing' with its last letter removed is 'DO IN'.
(Other definitions for do in that I've seen before include "Murder" , "Knock off" , "Get rid of" .)