Numbers game

Bill Belichick became known for the 3-4 defense, but even he's making a change. Harry How/Getty Images

ELVIS DUMERVIL DOESN'T have to say he's excited that the Broncos are using the 4-3 defense this year. His smile says it for him.

"I remember what it was like when we switched to the 3-4 in 2009," says Dumervil, a sixth-year defensive end with 43 career sacks. "They basically said, 'We're changing defenses. Good luck.'"

After the Broncos allowed a league-worst 29.4 PPG last season, it's not hard to understand why they're ditching the 3-4. But they aren't the only ones.

The Browns and Patriots have also dropped the scheme as their base defense. Make no mistake: Three-man fronts are not going away. The Packers, Steelers and 12 other teams still use them, but just a few years after the 3-4 seemed to be taking over the NFL, the pendulum is swinging back to the 4-3. Why?