Intrude using spring within lock (8)
I believe the answer is:
trespass
'intrude' is the definition.
(I know that intrude can be written as trespass)
'spring within lock' is the wordplay.
'spring' becomes 'spa' (spa can mean a mineral spring).
'within' indicates putting letters inside.
'lock' becomes 'tress' (both can mean a piece of hair).
'spa' inserted into 'tress' is 'TRESPASS'.
'using' is the link.
(Other definitions for trespass that I've seen before include "Invade" , "Enter land illegally" , "Wrongfully enter another's land" , "Illegal entry" , "Go where one shouldn't" .)