One is not bound to release spy (4,5)

I believe the answer is:

free agent

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'one is not bound' is the definition.
I can't tell whether this defines the answer.

'release spy' is the wordplay.
'release' becomes 'free' (synonyms).
'spy' becomes 'agent' (secret agent).
'free'+'agent'='FREE AGENT'

'to' is the link.

Can you help me to learn more?

(Other definitions for free agent that I've seen before include "Someone untied by a contract" , "who would be a gift to any actor seeking work?" , "Unrestricted actor" , "Nobody can force me" , "Someone acting without constraint" .)

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