Encroaches on step in locks (10)
I believe the answer is:
trespasses
'encroaches' is the definition.
(I've seen this in another clue)
'step in locks' is the wordplay.
'step' becomes 'pas' (I've seen this in another clue).
'in' is an insertion indicator.
'locks' becomes 'tresses' (I've seen this before).
'pas' placed within 'tresses' is 'TRESPASSES'.
'on' acts as a link.
(Other definitions for trespasses that I've seen before include "Forgive them" , "may they be forgiven!" , "Unlawfully enters" .)