Youth holding end of poodle’s leash (4)
I believe the answer is:
lead
'leash' is the definition.
(I know that leash can be written as lead)
'youth holding end of poodle's' is the wordplay.
'youth' becomes 'lad' (lad means a young man).
'holding' is an insertion indicator.
'end of' says to take the final letters.
The last letter of 'poodle' is 'e'.
'lad' enclosing 'e' is 'LEAD'.
(Other definitions for lead that I've seen before include ""bullets"" , "Short wire used as jumper - Pb" , "Guide; graphite" , "Toxic, malleable, metallic element" , "first guitarist" .)