Working outside West Indian state line is a detrimental move (3,4)
I believe the answer is:
own goal
'is a detrimental move' is the definition.
I can't judge whether this defines the answer.
'working outside west indian state line' is the wordplay.
'working' becomes 'on' (on can mean working or activated).
'outside' means one lot of letters goes inside another (some letters go outside others).
'west' becomes 'W' (abbreviation).
'indian state' becomes 'goa' (Goa is a state of India).
'line' becomes 'l' (used when specifying particular lines from a poem).
'on' enclosing 'w' is 'own'.
'own'+'goa'+'l'='OWN GOAL'
Can you help me to learn more?
(Other definitions for own goal that I've seen before include "Unfortunate football incident" , "Costly footballing error" , "Self-inflicted loss" , "A score against one's self or team" , "Football score at the wrong end" .)