Snapping a football is like turning the ignition key in your car. It's a simple procedure that gets things going, but when it doesn't work properly, the whole operation can sputter and conk out.

The Eagles found out Sunday just how major a seemingly minor act like the exchange between a center and quarterback can be when it isn't precise. They'll now have to figure out how detrimental it is to their Super Bowl aspirations to have lost Jamaal Jackson for the season.

The center tore the anterior cruciate ligament in his left knee in the first quarter of the 30-27 wipe-of-the-brow victory over the Broncos, Eagles coach Andy Reid confirmed yesterday. Jackson's injury created a domino effect that helped contribute to the Eagles' second-half unraveling.

Nick Cole slid over from right guard and replaced Jackson, while Max Jean-Gilles came off the bench to take Cole's spot. The shuffling affected the two primary responsibilities of offensive linemen - run-blocking and pass protection - but the most glaring consequence was Cole's shaky snapping of the football.

"It goes back to the miscues and miscommunications that we had," quarterback Donovan McNabb said. "I think for myself and Nick, it will be something which we'll work on all throughout the week."

There were three direct instances in which bad snaps caused a problem. On the first, Cole's pitch to DeSean Jackson, who was lined up in the shotgun in a Wildcat formation, was lobbed high. Jackson reached up for the ball, but the split-second hesitation appeared to doom the run. He was dropped for a 3-yard loss on third and 1, and the Eagles settled for a field goal.

In the second quarter, the Eagles faced another third down deep in Broncos territory. But Cole's shotgun snap to McNabb was slightly to the left and glanced off running back LeSean McCoy, who was in motion. The ball deflected into McNabb's hands, but he couldn't hang on and pounced on the fumble. Another field goal ensued.

The third errant snap was costly. With the Eagles backed up on their 1, on first down, Cole snapped the ball into his rear end. McNabb wasn't ready and fell on the loose ball. Reid said Cole started too soon.

"This week of practicing will help," Reid said. "It'll smooth those types of things out. We should be fine."

Even if the Eagles can eliminate the snap problems, there's still the timing issue to rectify. The offensive line was whistled for three false starts, and two seemed to be directly attributable to Cole's hesitation on when to snap.

"The biggest challenge for us is we're going to have to put in some extra work and get our communication down, because we had become so fluid with our communication and obviously something like this disrupts it," guard Todd Herremans said.

The running game skidded to a halt after Jamaal Jackson left. The Eagles gained 29 yards on six carries, a 4.8-yard average, during their opening drive and before the injury. Subtract McNabb's 27-yard fourth-quarter scramble and the Eagles managed just 49 yards on 18 carries, an average of 2.7 yards, the rest of the way.

Not all the blame can be pinned on the line. McCoy and Brian Westbrook chose the wrong running lanes on a few occasions. Tight end Alex Smith missed a block on a Leonard Weaver 2-yard run, and receiver Jason Avant whiffed on a block in the backfield, disrupting a Westbrook carry.

Jean-Gilles had perhaps the best block of the day when he pancaked Ryan McBean during McCoy's 11-yard tote in the third quarter. McBean got his revenge, however, when he dusted past Jean-Gilles in the fourth quarter and stopped Weaver after a marginal gain.

The pass protection was also noticeably different after Jackson departed, but the four sacks allowed - the most since the six against Oakland 10 games ago - weren't completely the line's fault.

Tackle Jason Peters was beat by the NFL leader, Elvis Dumervil, on the first sack, but the play - which resulted in a McNabb fumble - came before Jackson's injury. And there were two second-half sacks in which McNabb clearly had enough time to throw the ball away.

Still, Jamaal Jackson was a key to how the offense ran.

"It's obviously a big loss," Reid said. "He's a good football player."