Objection from pair initially on trial (7)
I believe the answer is:
protest
'objection' is the definition.
(protest is a kind of objection)
'pair initially on trial' is the wordplay.
'pair' becomes 'pr' (abbreviation).
'initially' says to take the initial letters.
'trial' becomes 'test' (synonyms).
The first letter of 'on' is 'o'.
'pr'+'o'+'test'='PROTEST'
'from' is the link.
(Other definitions for protest that I've seen before include "State objection" , "Express dissent" , "Objection from potters" , "Potters (anag.)" , "Express opposition" .)