ORCHARD PARK, N.Y. -- Keith Ellison has heard many times before that he's too small to effectively play linebacker in the NFL.
So it didn't bother him that the skeptics raised those concerns again last offseason, when the Buffalo Bills announced they were switching to a 3-4 defense, a scheme not particularly suited to someone with Ellison's 6-foot, 220-pound frame.
"According to most people, I'm not the prototypical-sized linebacker for any defense," Ellison said with a laugh Wednesday. "Football's football. My job is just to do whatever they ask of me."
It's a no-nonsense approach that has served Ellison well because -- for the fourth time in his five seasons in Buffalo -- he's being asked to make the jump from backup to a starting job.
Ellison will start Sunday alongside fellow middle linebacker Andra Davis when the Bills play at Green Bay. Ellison will be in the lineup after injuries have played havoc at the position.
Enter Ellison, the team's "Mr. Reliable," a 2006 sixth-round draft pick who has been a key injury-replacement, starting 38 games for the Bills -- at least seven in each of his four previous seasons.
Ellison started as a rookie in place of Takeo Spikes. In 2008, he took over after Angelo Crowell was hurt. And last year, he had at least one start at all three linebacker positions after a string of injuries struck the Bills' defense.
"This is old hat for me," Ellison said with a shrug. "I feel totally prepared. I've been the backup, and there's always somebody going down. So I've always been ready to step in."
This stint as a starter might represent Ellison's biggest challenge. He'll play in the middle of a scheme in which, unlike the 4-3 system, the linebacker is asked to directly take on linemen in defending against the run.
Ellison is aware of that, and he plans to rely on his quickness to shed blocks and reach the ball carrier.
Ellison was capable against the Dolphins. Taking over after Posluszny was hurt on the opening play of the third quarter, Ellison finished with six tackles on a Buffalo defense that gave up just three points and six first downs on Miami's seven second-half possessions.
Bills coach Chan Gailey emphasized that Ellison will receive most of the playing time because he's more accustomed to the system and showed during the offseasom that he can play the position.
"He's one of those guys who has instincts -- he's around the ball a lot," Gailey said. "He's doing a good job. The only thing he doesn't have is size. Everything else he's got."
Looking back, Ellison wasn't any more worried this year than in the past about making the Bills' roster, although he missed portions of spring minicamps and training camps because of a nagging injury.
"Antsy? Not too much, because you know it's out of your control," Ellison said. "It's nothing I could control, if they wanted to keep me or not. I thought I put my best effort forward."
Notes: Posluszny referred to his injury as a "slight sprain" and said he hopes to be back within a few weeks. He said he was hurt when his teammates landed on him as they gang-tackled Dolphins RB Ronnie Brown along the sideline. ... C Geoff Hangartner was held out of practice as a precaution after he hurt his left ankle against the Dolphins. Gailey said Hangartner will be evaluated to determine whether he can practice Thursday. ... RB Fred Jackson said his injured left hand has healed enough so that he doesn't intend to wear a protective pad, as he did Sunday.
Copyright 2010 by The Associated Press