Sucker pinching small brown horse (7)
I believe the answer is:
mustang
'horse' is the definition.
(mustang is a kind of horse)
'sucker pinching small brown' is the wordplay.
'sucker' becomes 'mug' ('mug' can be a synonym of 'sucker'**).
'pinching' is an insertion indicator (taking inside).
'small' becomes 's' (abbreviation - e.g. clothes size).
'brown' becomes 'tan' (tan is a kind of brown).
's'+'tan'='stan'
'mug' placed around 'stan' is 'MUSTANG'.
(Other definitions for mustang that I've seen before include "Small, wild US horse" , "Feral American horse" , "Wild horse of the West" , "Small feral horse of the US" , "one running wild" .)