First offender, note, caught by shop worker (9)
I believe the answer is:
stevedore
'worker' is the definition.
(stevedore is a kind of worker)
'first offender note caught by shop' is the wordplay.
'first offender' becomes 'eve' (I can't justify this - if you can you should believe this answer much more).
'note' becomes 'd' (musical note).
'caught by' indicates putting letters inside.
'shop' becomes 'store' (synonyms).
'eve'+'d'='eved'
'eved' inserted within 'store' is 'STEVEDORE'.
Can you help me to learn more?
(Other definitions for stevedore that I've seen before include "Dock-worker loads and unloads ships" , "Worker who loads and unloads ships" , "One is employed at a dock to load and unload ships" , "One loads and unloads ships" , "Unloader of shipping vessels" .)