Thief who is boss around the street (7)
I believe the answer is:
rustler
'thief' is the definition.
(I know that rustler is a type of thief)
'is boss around the street' is the wordplay.
'is boss' becomes 'ruler' (I can't explain this - if you can you should believe this answer much more).
'around' means one lot of letters goes inside another.
'the street' becomes 'st' (abbreviation).
'ruler' enclosing 'st' is 'RUSTLER'.
'who' acts as a link.
Can you help me to learn more?
(Other definitions for rustler that I've seen before include "One who takes livestock" , "Livestock thief" , "He stole cattle in the old west" , "lawbreaker" , "person taking stock" .)