Worker encountered me coming back first (5)
I believe the answer is:
emmet
'worker' is the definition.
(I've seen this before)
'encountered me coming back first' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'coming back' says the letters should be written in reverse.
'first' is a charade indicator (letters next to each other).
'me' backwards is 'em'.
'met' after 'em' is 'EMMET'.
(Other definitions for emmet that I've seen before include "Robert ...., .... Bergin," , "Robert, Irish patriot" , "social worker" , "tourist in the South West" , "Dialect word for an ant" .)