If it were true that sports build character then all athletes would be of good character. But this is not the case because sports don't build character, they reveal it.
Character is revealed by how an athlete reacts to a win. Is he taunting, trash-talking, or gloating ? Or is he humble? Does he credit his coach and teammates? What does he say about his opponent? Oscar de la Hoya after a win or a loss always showed good character. He would approach his opponent, hug him and compliment him. Floyd Mayweather, on the other hand, seemed to do the opposite. After a win over Victor Ortiz, he goes into a foul-mouthed rant aimed at Larry Merchant.
Character is also revealed by how an athlete reacts to a loss. Does he accept the outcome without complaint or excuses? Does he offer a congratulations to the other team? Or does he get angry and display a bad attitude? Skateboarders are the greatest losers. For example, when Tony Hawk pulled the 900 during best trick, there was a collective rejoicing amongst those who didn’t win.
During the competition, when the athlete is under pressure his character is brought forth. When he gets knocked down, does he get back up. Does he retaliate? Does he put himself before the team? Does he respect the call of the referee. John McEnroe would throw his tennis racquet every time he didn't like the referee's call. Good or bad, this is character revealed. It was always there. Take a look at Lance Armstrong. He's an athlete that had to win at all costs. He was doping and when he was caught, he lied until the evidence just got to be too much. How about Tonya Harding. She had her ex-husband take out the competition with a metal baton to her knee. There is a lot of this going on in sports these days. Is this character building? Of course there are athletes that displayed good character. George Foreman went back into boxing in his 40's to raise money for his church.