Objection can intervene (4,2)
I believe the answer is:
butt in
'intervene' is the definition.
(thesaurus)
'objection can' is the wordplay.
'objection' becomes 'but'.
'can' becomes 'tin' ('tin' can be a synonym of 'can').
'but'+'tin'='BUTT IN'
(Other definitions for butt in that I've seen before include "Interrupt or meddle - head first?" , "Interrupt or meddle - like goat?" , "Interrupt, intrude" , "Interrupt a conversation" , "Thrust oneself into a conversation" .)