It was barely a month into his N.B.A. career when Willy Hernangomez began to build a reputation for himself as a physical and fearless player. When the Knicks faced Atlanta’s Dwight Howard, Hernangomez pushed and prodded and defended until Howard, one of the league’s great redwoods, finally had had enough, throwing an elbow at Hernangomez.

Hernangomez barely flinched. “Maybe he felt pain in his elbow,” he mused afterward.

In a way, none of what happened that afternoon was a surprise. By now, Knicks teammates and Hernangomez’s parents have felt the impact of his toughness on the court. As a teenager, he and his brother, Juan, would play basketball against his parents, but those battles ended quickly. In one game, his mother, a former Spanish Olympian, guarded him and fouled him. When Willy was on offense on the next possession, he hit her in the face with his elbow, bloodying her nose.

They have not played since.

“She told me, ‘Willy, I’m your mom,’” he said recently. True enough, except for one problem. “I want to fight in the practice, in the games,” he said.

That aggressive streak has helped land Hernangomez in the N.B.A. at the age of 22. In this, his rookie season, he has been a pleasant surprise for a club that thought it would essentially rely on the newly acquired Joakim Noah at center. Instead, the 7-foot Hernangomez — not 6-11, as he is listed — has averaged 13.1 minutes per game and displayed a knack for rebounding and the low post.