“And when I saw that you did not save me, I put my life in my hand, and passed over against the children of Ammon and Yahweh delivered them into my hand.”
Thus Gilead and he had done the only thing they could. Recognising that they would receive no assistance from the tribal confederacy they had taken matters into their own hands. Under his leadership they had taken the risk, trusted to their own sword arm and had attacked the children of Ammon, and with Yahweh's strong help had been victorious. Note how proudly he speaks of his people in terms of himself. He was enjoying being judge of Gilead.
“Why then are you come up to me this day to fight against me?”
Like the strong man he was, and in the same way that he had done to Ammon, he showed his enemies that they were in the wrong. Let them consider well and give good reason for fighting against him. They should rather be thanking him, for Ammon had also made attacks on Ephraim (Judges 10:9).