Stop over to join regulars in boozer (4)
I believe the answer is:
oboe
'stop' is the definition.
(thesaurus)
'over to join regulars in boozer' is the wordplay.
'over' becomes 'o' (cricket abbreviation).
'to join' is a charade indicator (letters next to each other).
'regulars in' indicates alternate letters.
The alternate letters of 'boozer' are 'boe'.
'o'+'boe'='OBOE'
(Other definitions for oboe that I've seen before include "Reed instrument" , "Musical instrument" , "blow it!" , "issuer of notes" , "music producer" .)