I attempt to follow gang in criminal activity (8)
I believe the answer is:
banditry
'criminal activity' is the definition.
(I've seen this before)
'i attempt to follow gang' is the wordplay.
'attempt to' becomes 'try' (I've seen this in other clues).
'follow' means one lot of letters go next to another.
'gang' becomes 'band' (both can mean a group of people).
'i'+'try'='itry'
'itry' after 'band' is 'BANDITRY'.
'in' is the link.
(Other definitions for banditry that I've seen before include "Activity of lawless robbers" , "Brigandage" , "robbery" , "Activity of armed robbers" , "Criminal behaviour" .)