Cam Newton is not the only Super Bowl quarterback who has shown he doesn't take losses in stride.
In his 2013 Sports Illustrated Sportsman of the Year story from December 2013, SI's Lee Jenkins reveals that Peyton Manning was a fierce competitor as a kid. He didn't always take losses well.
From the SI Vault:
Sportsmanship wasn't always his specialty. When Manning was five and his coach-pitch team lost every game by about 20 runs, the coach would invariably tell the boys it was a tie. "He thinks we're stupid," Manning griped to his parents. "It was not a tie." When he was eight and Archie coached his youth basketball team, they sparred because Archie drafted his friends' sons even though many of them couldn't shoot. Archie vowed never to coach him again. When Peyton was 12 he had a new basketball coach with a curious substitution pattern. After one loss, the coach told the team, "The reason we didn't win the game is because you weren't ready to play." Manning pointed a finger in his face. "No," he protested, "the reason we didn't win the game is because you don't know what you're doing." Archie drove him to the coach's house that night, in tears, to apologize.
Though things have changed a bit, Manning’s competitive spirit has never quite waned.