Amazing goals! Newcastle's first catchphrase (6)
I believe the answer is:
slogan
'catchphrase' is the definition.
(I've seen this before)
'amazing goals newcastle's first' is the wordplay.
'amazing' is an anagram indicator.
'first' says to take the initial letters.
The first letter of 'newcastle' is 'n'.
'goals' is an anagram of 'sloga'.
'sloga'+'n'='SLOGAN'
(Other definitions for slogan that I've seen before include "War cry - advertising jingle" , "'Motto, watchword (6)'" , "Identifying catchword" , "Advertising catchphrase" , "Marketing phrase" .)