The father of Austin Metcalf, the teenager killed after being stabbed in the heart at a high school track meet, has made a desperate plea. Metcalf’s death made headlines around the world after the 17-year-old was knifed during an altercation at a track and field championship at Kuykendall Stadium in Frisco, Texas on April 2. 18-year-old Karmelo Anthony was arrested and charged with first-degree murder following the incident, said to have been caused by an argument over seats in the…