Market leaders in zero alcohol ale stocked by boozer (6)
I believe the answer is:
bazaar
'market' is the definition.
(bazaar is a kind of market)
'leaders in zero alcohol ale stocked by boozer' is the wordplay.
'leaders in' indicates taking the first letters.
'stocked by' is an insertion indicator.
'boozer' becomes 'bar'.
The initial letters of 'zero alcohol ale' is 'zaa'.
'zaa' placed into 'bar' is 'BAZAAR'.
(Other definitions for bazaar that I've seen before include "Oriental market place" , "exchange ..." , "An open oriental-type market" , "Charity sale of many different things" , "Where many would shop" .)