Charles Ellicott Commentary Genesis 32:25

"And when he saw that he prevailed not against him, he touched the hollow of his thigh; and the hollow of Jacob`s thigh was strained, as he wrestled with him." — Genesis 32:25 (ASV)

The hollow of Jacob’s thigh was out of joint. — The hollow is in the Hebrew the pan or socket into which the end of the thigh bone is inserted, and the verb more probably signifies that it was sprained from the over-tension of the muscles in the wrestling.

But, in spite of his sprained tendons, Jacob still resisted and could not be thrown down, and the angel, unable to gain any further advantage, at last acknowledges Jacob’s superiority, and at sunrise craves permission to depart.