Fish causing awful New York havoc (7)
I believe the answer is:
anchovy
'fish' is the definition.
(anchovy is a kind of fish)
'awful new york havoc' is the wordplay.
I cannot really see how this works, but
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is found in the answer.
an anagram of 'havoc' is 'achov' which is present in the remaining letters.
A single letter 'y' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
'causing' is the link.
Can you help me to learn more?
(Other definitions for anchovy that I've seen before include "Small edible fish" , "Little fish, usually tinned or salted" , "Small salty fish" , "Strong-flavoured fish" , "Tiny fish, usually canned" .)