NATAL, Brazil — The most ruthless soccer players often use their hands or elbows or knees to rough up opposing players. The most reckless — or dirtiest — might even use their cleats. Then there is Luis Suárez.

Suárez, the Uruguayan striker who has emerged as one of the best players in the world over the past year, is a biter. And, it seems, a serial one.

For the third time in his career, Suárez is facing potential punishment for appearing to sink his teeth into an opponent. This time, it happened on the biggest soccer stage of all, the World Cup, during Uruguay’s 1-0 victory over Italy on Tuesday. Late in the second half, Suárez bumped into Giorgio Chiellini, an Italian defender, while jockeying for position in the penalty area and then dropped his head into Chiellini’s shoulder. Chiellini immediately recoiled as both fell to the ground.

The scene was surreal: The referee — a Mexican named Marco Rodríguez, whose nickname is Dracula because of his resemblance to a version of that character on Mexican television — did not notice and paid no mind to Chiellini’s attempts to pull his collar aside to show what appeared to be bite marks on the back of his left shoulder.