I am an Amalekite - Dr. Delaney remarks that an Amalekite took that crown from off the head of Saul, which he had forfeited by his disobedience in the case of Amalek.

And he said unto me, Who [art] thou? And I answered him, I [am] an (c) Amalekite.
(c) He was an Amalekite born, but renounced his country and joined with the Israelites.

And he said unto me, who art thou?.... Being willing to know whether a friend or an enemy, which by his coming behind him he could not tell:
and I answered him, I am an Amalekite: which he might be; but it is not likely he should tell Saul he was, which would not recommend him to him; though indeed he was now in such circumstances, that the Amalekites had nothing to fear from him; and if he was slain by him, as Josephus (f) affirms he was, it seems to be a just retaliation on him for sparing any of that race, contrary to the will of God.
(f) Antiqu. l. 6. c. 14. sect. 7.