Support grabbed by young chap - or a dog (8)
I believe the answer is:
labrador
'a dog' is the definition.
(I've seen this before)
'support grabbed by young chap or' is the wordplay.
'support' becomes 'bra' (a support for the breasts).
'grabbed by' means one lot of letters goes inside another.
'young chap' becomes 'lad' (I've seen this before).
'bra' inserted within 'lad' is 'labrad'.
'labrad'+'or'='LABRADOR'
(Other definitions for labrador that I've seen before include "Newfoundland area; dog" , "Spaniard who works" , "Bar a lord from Canada" , "Breed of 1 across" , "One that may have gone out with the guns" .)