Small snake corners large one who makes you bridle (7)
I believe the answer is:
saddler
'one who makes you bridle' is the definition.
'small snake corners large' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'snake' becomes 'adder' (adder is a kind of snake**).
'corners' is an insertion indicator.
'large' becomes 'l'.
'adder' going around 'l' is 'addler'.
's'+'addler'='SADDLER'
(Other definitions for saddler that I've seen before include "he'll offer you a seat" , "Maker of horse's equipment" , "Leather-worker" , "One makes leather goods for horses" , "Maker of seats for riders" .)