Occasions for choosing before once between judge and new attorney (9)
I believe the answer is:
referenda
'occasions for choosing' is the definition.
(plural of referendum)
'before once between judge and new attorney' is the wordplay.
'before once' becomes 'ere' (archaic word for 'before').
'between' means one lot of letters goes inside another.
'judge' becomes 'ref'.
'and' becomes 'n' (common abbreviation for 'and').
'new attorney' becomes 'da' (District Attorney. I am not sure about the 'new' bit.**).
'ref'+'n'='refn'
'ere' going within 'refn' is 'referen'.
'referen'+'da'='REFERENDA'
(Other definitions for referenda that I've seen before include "National polls as for amendments of constitution" , "General votes" , "decisions for people" , "National votes or plebiscites (9)" , "Votes put to country generally 9)" .)