Fisher heads off homicidal Bostonian (6)
I believe the answer is:
angler
'fisher' is the definition.
(angler is a kind of fisher)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for angler that I've seen before include "Fisher with hook and line." , "Sportsman" , "person hoping to catch fish" , "who looks for compliments" , "Strait; -- of Lochalsh" .)