Break in spring found in lock (8)
I believe the answer is:
trespass
'break in' is the definition.
(thesaurus)
'spring found in lock' is the wordplay.
'spring' becomes 'spa' (spa can mean a mineral spring).
'found in' means one lot of letters goes inside another.
'lock' becomes 'tress' (both can mean a piece of hair).
'spa' inserted within 'tress' is 'TRESPASS'.
(Other definitions for trespass that I've seen before include "Enter another's property unlawfully" , "Encroachment" , "Enter someone's property unlawfully" , "Illegal entry" , "Go out of bounds" .)