First of visitors obscuring entrance in pub is outspoken (5)
I believe the answer is:
vocal
'is outspoken' is the definition.
(synonyms)
'first of visitors obscuring entrance in pub' is the wordplay.
'first of' suggests taking the first letters.
'entrance in pub' becomes 'cal' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The first letters of 'visitors obscuring' is 'vo'.
'vo'+'cal'='VOCAL'
(Other definitions for vocal that I've seen before include "speaking loudly" , "For, giving, voice" , "Relating to the human voice" , "Articulate" , "Spoken" .)