MCKINNEY, Texas — High school track star Karmelo Anthony was asked 15 times to leave the tent for an opposing team but “refused” to — allegedly sparking the deadly stabbing of fellow teen Austin Metcalf last year, a witness testified Friday. The witness, a 17-year-old Frisco Memorial High School student, explained that he and at least six others were under their school’s team tent when he saw Anthony in their area wearing the opposing Frisco Centennial High School gear. Memorial students