Young man accepts one put down (4)
I believe the answer is:
laid
'put down' is the definition.
(to lay something is to put it down somewhere)
'young man accepts one' is the wordplay.
'young man' becomes 'lad' (lad can mean a boy or young man).
'accepts' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'lad' going around 'i' is 'LAID'.
(Other definitions for laid that I've seen before include "Produced (an egg)" , "tables may be?" , "Deposited" , "Prepared (a trap)" , "Flattened by wind and rain" .)