Why do athletes choke under pressure?

The siren has sounded. The scores are even. A footy player has one final chance to kick an easy goal to get his team into the finals. He’s right in front of the goals. He lines up. Kicks. Misses. The pressure of such a moment was phenomenal, and the player choked under it. So what happens in the brain during such intense periods? Why can some people remain calm while others can’t handle it? If you're keen to listen to another episode, check out Wanted: Unicorns. Mission: Mars.