Intrude with spring breaking lock (8)
I believe the answer is:
trespass
'intrude' is the definition.
(I know that intrude can be written as trespass)
'spring breaking lock' is the wordplay.
'spring' becomes 'spa' (spa can mean a mineral spring).
'breaking' indicates putting letters inside.
'lock' becomes 'tress' (both can mean a piece of hair).
'spa' put into 'tress' is 'TRESPASS'.
'with' acts as a link.
(Other definitions for trespass that I've seen before include "Sin (archaic)" , "Enter another's property without permission" , "Enter someone's property unlawfully" , "Wrongfully enter another's land" , "sin in the eyes of the church" .)