NASHVILLE, Tenn. (AP) — Defending champions Alexa Knierim and Brandon Frazier withdrew from the U.S. Figure Skating Championships on Wednesday night when he tested positive for COVID-19. The pairs event begins Thursday at what amounts to the U.S. trials for the Beijing Olympic team. Knierim and Frazier, who became a duo last season when her husband, Chris, retired from skating still could be selected for the games. They would need to petition to a selection committee and prove they are fit to be chosen. The United States has two spots in the pairs field for China.