An ailing teenager trying to bow out of football practice early was ordered back to the gridiron — and his death, a lawyer claims. Nicholas Dellaventura, 15, eventually collapsed at the end of a preseason practice in Staten Island last year and died hours later of heat stroke, as his body temperature surged to 110 degrees, his family claims. A star freshman on St. Joseph by-the-Sea High School’s junior varsity team, Nicholas was aiming for a bigger role with the squad when he joined the July 23 drills at the school. But the 5-foot-8, 210-pound offensive lineman struggled in the mid-80s heat and high humidity, and at one point paused, his family claims. But instead of letting him take off a few plays or leave practice, coach Salvatore Ferraioli — who resigned a month later when he was arrested in the federal takedown of a Gambino gambling ring — shouted something that prompted the determined athlete to get back on the field, attorney Ralph DeSimone told The Post.