Muscle resistance seen in retired player (9)
I believe the answer is:
retractor
'muscle' is the definition.
(I've seen this before)
'resistance seen in retired player' is the wordplay.
'resistance' becomes 'r' (abbreviation).
'seen in' is an insertion indicator.
'retired' becomes 'ret' (e.g. following the name of a retired army officer).
'player' becomes 'actor' ('actor' can be a synonym of 'player'**).
'ret'+'actor'='retactor'
'r' put within 'retactor' is 'RETRACTOR'.
(Other definitions for retractor that I've seen before include "that springs back in reverse?" , "One withdraws" , "Instrument" , "Muscle" , "It must pull back" .)