Restrain worker on strike (8)
I believe the answer is:
handcuff
'restrain' is the definition.
(I know that handcuff is a kind of fetter)
'worker on strike' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'strike' becomes 'cuff' (both can mean to hit).
'hand'+'cuff'='HANDCUFF'
(Other definitions for handcuff that I've seen before include "Put bracelets on" , "Restrict movement" , "Restrain (one arrested)" , "Shackle by the wrist" , "Restraint" .)