They get shot at, causing great upheaval in backstreet (7)
I believe the answer is:
targets
'they get shot at' is the definition.
The definition suggests an adverb but the answer is not.
'great upheaval in backstreet' is the wordplay.
'upheaval' is an anagram indicator.
'in' means one lot of letters goes inside another.
'backstreet' becomes 'ts' ('st' backwards).
'great' anagrammed gives 'arget'.
'arget' inserted inside 'ts' is 'TARGETS'.
'causing' is the link.
Can you help me to learn more?
(Other definitions for targets that I've seen before include "Butts" , "Goals" , "objectives of firing people" , "Aim points" , "Reference points to shoot at" .)