PHILADELPHIA -- Even in perfect weather, some footballs can be too slippery.

While teams are allowed to practice with regular game balls during the week, the ones used on special teams are off limits until shortly before kickoff. They're shiny and new, and even have a name -- the K-Ball.

One major problem, though: The balls are a bit slick because they're fresh out of the box.

"They're slicker than the plastic balls my kids play with," injured Philadelphia Eagles long-snapper Mike Bartrum said Tuesday.

Since 1999, kickers, punters, holders and snappers have complained to anyone who will listen that they don't like the K-Balls.

It took Tony Romo's bobbled snap to really get everyone's attention.

Romo led Dallas to the playoffs after replacing Drew Bledsoe as the starting quarterback and earned a trip to the Pro Bowl. But he'll be remembered for mishandling the snap on a 19-yard field goal in the closing moments of the Cowboys' 21-20 loss to the Seahawks in a wild card playoff game Saturday.

The NFL introduced the K-Balls eight years ago after the competition committee decided teams were abusing their privileges and taking unusual measures to condition balls to fly higher and travel farther.

Kickers and punters were accused of using strange methods to soften the leather, spread the seams and inflate the bladder. Rumors included instances of balls being put in microwave ovens, dryers and saunas.

"The reason this was put in place was to prevent teams from doctoring balls for kicking," league spokesman Greg Aiello said.

So the night before a game, 12 balls marked with a "K" are delivered straight from the manufacturer, Wilson Sporting Goods, to the officials. Two hours before the game, a representative from each team can prepare the balls by rubbing them down and brushing them off. An official then checks the air pressure, puts the balls in a bag and subs them in on kicks.

A day after Romo's bobble, David Akers kicked a 38-yard field goal as time expired to give the Eagles a 23-20 victory over the New York Giants in the NFC's other wild-card game.

Though Romo didn't make any excuses for his gaffe, Akers and others around the league blamed the K-Ball.

"Kicking balls are very, very slick," Akers said. "They have a lot of wax on them because they are brand new. You don't get to work them in very much, and you see a lot of that happening."

BRONCOS FIRE COYER: The Denver Broncos fired defensive coordinator Larry Coyer on Tuesday, nine days after a once-promising season sputtered to a close with five losses in seven games.

Coyer oversaw a defense that started this season by becoming the first team in 64 years to not allow a touchdown over the first 11 quarters. But the squad faltered, finishing 14th in the league in yards allowed as the Broncos stumbled from a 7-2 start to finish 9-7.

HORN QUESTIONABLE: Four-time Pro Bowl receiver Joe Horn sat out significant portions of the New Orleans Saints' practice, still bothered by the groin injury that caused him to miss the past four games.

Saints coach Sean Payton said Horn, who had a pair of big touchdown catches in a victory over Philadelphia earlier this season, is questionable for the rematch Saturday night in the second round of the NFC playoffs.

"I was disappointed he wasn't able to practice," Payton said. "I think he's doing everything he can to get ready."

EXTRA POINTS: New Falcons coach Bobby Petrino reached agreements with Dallas defensive coordinator Mike Zimmer and Cincinnati receivers coach Hue Jackson to be his right-hand men in Atlanta. ... Pittsburgh Steelers assistant Russ Grimm was interviewed as the final candidate to replace the fired Dennis Green as Arizona Cardinals head coach. ... The Saints brought back kickoff specialist Billy Cundiff for the playoffs.