Ravens lose more than a center in Birk

The Baltimore Ravens' Matt Birk, who announced his retirement Friday, will be remembered as one of the best centers of his generation. But Birk's credentials go beyond going to six Pro Bowls and being part of nine playoff teams.

He was a high-character guy in the locker room who always exuded toughness. Despite injuries to his hip, neck and knee, he never missed a game in his four seasons in Baltimore and leaves after starting 112 straight games, the NFL's longest active streak among centers.

Birk was committed to the community, which is why it's not a surprise that he announced his retirement during a community event at a Baltimore elementary school. Last year, he received the NFL's Walter Payton Man of the Year award, which recognizes his work on and off the field. His foundation reaches close to 100,000 children in the Baltimore area and motivates students to read at home through an incentive-based system.

Birk is the first player to show initiative when it comes to concussions and the effect on the body. Three years ago, he pledged to donate his brain and spinal cord tissues after death to a Boston University medical school program that studies sports brain injuries. During the lead-up to the Super Bowl, Birk urged other players to do the same.

But not all players are like Birk. A sixth-round pick out of Harvard, Birk went on to be a starter for 12 seasons and was named to the all-decade team (2000s). After struggling in 2012, he bounced back last season at age 36 and was part of an offensive line that was key in protecting quarterback Joe Flacco in the postseason. Winning his first Super Bowl was a fitting conclusion to Birk's 15-year career.

"Matt Birk was one of the greatest people I've ever played with ... truly a great role model and parent ... very fortunate to be his teammate," Ravens wide receiver Torrey Smith posted Friday on Twitter.

The Ravens are expected to go with Gino Gradkowski, a fourth-round pick in 2011, at center. While this may fill Birk's spot in the starting lineup, the Ravens will be hard-pressed to replace Birk's impact elsewhere.