Eagles adjust after Marlin Jackson injury

PHILADELPHIA -- About midway through the Eagles’ practice Tuesday, everything stopped. The only sound was the low hum of the practice facility exhaust fans, sucking the humid air into the steamy South Philadelphia atmosphere.

All eyes were on fallen free safety Marlin Jackson, who took off his gloves and threw them to the artificial surface in disgust. Jackson, a former Colts cornerback who is recovering from reconstructive surgery in both knees and trying to adjust to his new role as the Eagles’ starting free safety, then got up and was helped to the sideline, where he leaned his head against the gray wall and starting wailing in frustration and pain.

Practice quickly resumed after Jackson left the field and it was next man up -- rookie Nate Allen, the Eagles’ second-round draft pick. Not an ideal situation.

After practice, the Eagles announced that Jackson had suffered an ankle injury -- not another knee blowout -- which was of some relief. But the way Jackson reacted, it was clear the injury was serious, meaning the Eagles’ first great experiment to fix a defense that underachieved in 2009 has suffered a serious setback. (Note: Jackson ruptured his Achilles tendon and is out for the season.)

Defensive coordinator Sean McDermott was asked what this means for the free safety position. He just shook his head, obviously upset about the injury to Jackson, who was signed to a one-year free-agent deal and attacked his new position with consistent vigor and a constant smile.

"We’ll just have to see what happens with Marlin," said McDermott, not sounding too optimistic.

Without Jackson, the Eagles may be forced to submit a rookie to the rigors of the free safety spot for the second straight year. After perennial Pro Bowler Brian Dawkins was allowed to leave for Denver last spring, the Eagles tried converting rookie corner Macho Harris into a free safety. That didn’t work. Veterans Quintin Demps and Sean Jones were given a shot. Nothing worked.

At least Allen played safety at South Florida. But McDermott’s defense is very aggressive -- the Eagles blitzed on 41 percent of the called pass plays last year, sixth most in the league -- and often leaves the secondary vulnerable to big plays. Breaking down protection only works if you protect the house on the back end, and the Eagles gave up 15 touchdown passes off the blitz last year, second most in the league.

After practice, Allen was surrounded by reporters trying to measure his reaction to Jackson’s injury.

"All I know right now is I’ve got a lot of work to do," said Allen. "I’ve got a lot to learn. I’ve got to learn the whole system. So much of it is blurry. I need to get it down so I can play fast. That’s the point. That’s what you want to do."

The learning curve for Allen just got a lot steeper.