Punt, not the first that is set free (5)
I believe the answer is:
untie
'set free' is the definition.
(I've seen this before)
'punt not the first that is' is the wordplay.
'not the first' means to remove the first letter.
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'punt' with its initial letter taken off is 'unt'.
'unt'+'ie'='UNTIE'
(Other definitions for untie that I've seen before include "Open a knot" , "resolve" , "Free from restraining bonds or ropes" , "Separate" , "Loose bonds" .)