Believers in AA run it out, initially sceptical (10)

'believers' is the definition.
The answer and definition can be both people as well as being plural nouns.
Perhaps you can see an association between them that I can't see?

'in aa run it out initially sceptical' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'initially' indicates taking the first letters.
The initial letter of 'sceptical' is 's'.
'in'+'aa'+'run'+'it'='inaarunit'
'inaarunit' is an anagram of 'unitarian'.
'unitarian'+'s'='UNITARIANS'

Can you help me to learn more?