Attack in street, thinking to disregard offence (3)
I believe the answer is:
mug
'attack in street' is the definition.
(to mug someone is to rob them in the street)
'thinking to disregard offence' is the wordplay.
'thinking' becomes 'musing' (muse can mean to think about something).
'to disregard' is a deletion indicator.
'offence' becomes 'sin' (a sin is an offence or transgression).
'musing' with 'sin' taken out is 'MUG'.
(Other definitions for mug that I've seen before include "Fall guy" , "concentrate on studying" , "Make a face" , "Slangy victim, by gum" , "In slang, a person easily deceived" .)