Old rocker -- one to be locked up, restrained (4)
I believe the answer is:
tied
'restrained' is the definition.
(tying is a kind of restraining)
'old rocker one to be locked up' is the wordplay.
'old rocker' becomes 'ted'.
'one' becomes 'i' (Roman numeral).
'to be locked up' indicates putting letters inside.
'ted' enclosing 'i' is 'TIED'.
(Other definitions for tied that I've seen before include "In no-win situation" , "Bound or secured" , "have equal scores" , "eg Scored 1-1" , "Bound; placed equal" .)