On set, Piers cut off abruptly when about to butt in (9)
I believe the answer is:
interpose
'to butt in' is the definition.
(I've seen this before)
'on set piers cut off' is the wordplay.
'cut' means to remove the last letter.
'off' indicates anagramming the letters.
'on'+'set'+'piers'='onsetpiers'
'onsetpiers' with its final letter taken off is 'onsetpier'.
'onsetpier' anagrammed gives 'INTERPOSE'.
'abruptly when about' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for interpose that I've seen before include "Muscle in" , "butt in" , "step in" , "Insert between (one thing and another)" , "mediate" .)