Spring in lock giving illegal entry (8)
I believe the answer is:
trespass
'illegal entry' is the definition.
(I've seen this before)
'spring in lock' is the wordplay.
'spring' becomes 'spa' (I've seen this before).
'in' indicates putting letters inside.
'lock' becomes 'tress' (I've seen this before).
'spa' inserted into 'tress' is 'TRESPASS'.
'giving' acts as a link.
(Other definitions for trespass that I've seen before include "Go where one shouldn't" , "Go out of bounds" , "Enter someone's property unlawfully" , "Encroachment" , "Wrongfully enter another's land" .)