'Small beer' — second fellow's description of Miller's Willy (8)
I believe the answer is:
salesman
'description of miller's willy' is the definition.
(Willy appears in Miller's play Death of a Salesman)
'small beer second fellow's' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'beer' becomes 'ale' (I've seen this before).
'second' becomes 's' (common abbreviation).
'fellow' becomes 'man' (I've seen this before).
's'+'ale'+'s'+'man'='SALESMAN'
(Other definitions for salesman that I've seen before include "Slam Sean badly for his selling" , "Famous play by Arthur Miller 'Death of a . . . . . . . .'" , "Company representative" , "Amen, lass, to the seller" , "He used to be known as a commercial traveller" .)