Posted by ESPN.com's Kevin Seifert
Williamson said he believes Birk, 32, has "lost a little pop" from his prime but still should be considered one of the top 10 centers in the league. There will be some drop-off in talent no matter who replaces Birk, Williamson said, but the biggest concern for the Vikings is the more general loss of a player who had started 48 consecutive games at the position.
Williamson: I think he'll be missed as much for his leadership and line calls than anything else. What the average fan doesn't realize is that continuity is almost as important as talent on the offensive line. Knowing what the guy on the left or the right is going to do really goes a long way. It wouldn't shock me if the Vikings end up with new starters on the line, at center and also maybe at right tackle. That's a pretty big deal. The continuity aspect of doing that is the real concern.
You look at that division, and it used to be that the defenses there weren't too hard to decipher. But now you've got Green Bay going to a 3-4. You've got the new coach in Detroit [Jim Schwartz], and he's a defensive-minded guy who is going to throw some wrinkles in there. So more than ever, you need that leadership and intelligence from the center. From that perspective, this loss would be worrisome if I were the Vikings.
I think that's a sensible way of looking at Birk's decision to sign with Baltimore. Birk didn't make the Pro Bowl last season and probably didn't deserve to. But part of evaluating this move is judging what will come behind him. The Vikings likely will give backup John Sullivan the first chance to win the job, but his next NFL start will be his first. Sullivan -- or whoever replaces Birk -- will be the fulcrum for measuring the impact of this loss.