Ultimately Vernon Kay confused American (4)
I believe the answer is:
yank
'american' is the definition.
(Yank can informally mean an American)
'ultimately vernon kay confused' is the wordplay.
'ultimately' suggests the final letters.
'confused' is an anagram indicator.
The final letter of 'vernon' is 'n'.
'n'+'kay'='nkay'
'nkay' is an anagram of 'YANK'.
(Other definitions for yank that I've seen before include "Statesman?" , "Tug sharply - American" , "Pull with a sudden movement" , "Big jerk!" , "Sudden hard pull" .)