Auckland, New Zealand

The Rugby World Cup has its exclusive club of bluebloods. Only four teams—New Zealand, Australia, South Africa and England—have ever won this tournament, and they've produced 11 of the 12 finalists. It's an elite group that shuns new members.

But as the 2011 tournament reaches the knockout stage this weekend, the team everyone's talking about is Ireland. With a surprising surge, the Irish have blitzed through the group stage, beating Australia 15-6 and becoming the talk of world rugby. It's not just that the Irish are unlikely contenders (Ireland has never really won much of anything before). What makes this team special is something that's unusual in any sport, and exceedingly rare in a royal and ancient game like rugby: a sprig of genuine innovation.

The secret behind Ireland's surge is a revolutionary and suffocating defensive scheme, known as the "choke," that relies on ferocious tackling and a loophole in the rules of the game to sap energy and momentum of its opponents. As Ireland prepares for a quarterfinal matchup with Wales on Saturday, this new system has confounded opponents and transformed a struggling team into contenders for the sport's biggest prize.

"Ireland didn't come into this World Cup as big favorites because they lost all four of their [pre-event exhibition] games, but they've got a team that can knock over anyone," said Nick Mallett, Italy's head coach. "I don't think any team could be confident of playing Ireland at the moment."