Barrister? A senior one faces pressure (7)
I believe the answer is:
pleader
'barrister?' is the definition.
(I know that pleader is a type of barrister)
'a senior one faces pressure' is the wordplay.
'a senior one' becomes 'leader' (someone in charge).
'faces' says to put letters next to each other (some letters face or go next to others).
'pressure' becomes 'p' (abbreviation).
'leader' put after 'p' is 'PLEADER'.
(Other definitions for pleader that I've seen before include "case is made by one" , "Person making case" , "Pale red (anag.)" , "one making earnest entreaty" , "Advocate" .)