Periodically scratched, plain carpet is free (8)
I believe the answer is:
liberate
'is free' is the definition.
(I've seen this before)
'periodically scratched plain carpet' is the wordplay.
'periodically scratched' indicates alternate letters (letters scratched out periodically).
'carpet' becomes 'berate' (I've seen this before).
The alternate letters of 'plain' are 'li'.
'li'+'berate'='LIBERATE'
(Other definitions for liberate that I've seen before include "let go" , "Make free" , "Free (someone)" , "Set free, emancipate" , "Set free, release from slavery" .)