Season doesn't start terribly free, so butt in (9)
I believe the answer is:
interfere
'butt in' is the definition.
(I've seen this before)
'season doesn't start terribly free' is the wordplay.
'season' becomes 'winter' (winter is a season).
'doesn't start' means to remove the first letter.
'terribly' indicates an anagram.
'winter' with its first letter removed is 'inter'.
'free' with letters rearranged gives 'fere'.
'inter'+'fere'='INTERFERE'
'so' is the link.
(Other definitions for interfere that I've seen before include "Obstruct, pry" , "Poke one's nose in" , "Meddle, intrude" , "Attempt" , "Meddle in someone else's business" .)