Duck and swan unrestricted (4)
I believe the answer is:
open
'unrestricted' is the definition.
('open' can be similar in meaning to 'unrestricted')
'duck and swan' is the wordplay.
'duck' becomes 'o'.
'and' says to put letters next to each other.
'swan' becomes 'pen' (pen is a kind of swan).
'o'+'pen'='OPEN'
(Other definitions for open that I've seen before include "Not secret or hidden" , "Not closed or obstructed" , "simple" , "Not closed or secret" , "This championship includes both professional and amateur golfers" .)