It's not exactly a secret that the Buffalo Bills haven't been able to stop the run over the last two seasons. The team had the 30th-ranked run defense in the NFL in 2009, surrendering 156.3 rushing yards per game. They'd have taken that level of production in 2010, when that average jumped to 169.6 yards per game - good enough to rank the Bills dead last in the league.
The folks at Football Outsiders have further clarified some of Buffalo's struggles against the run, as several Bills defenders ranked near the bottom of the league in run stop rate. FO has an explanation of the metric at that link, but in essence, it measures the number of stops a defender makes short of acceptable yards allowed on a specific down.
At linebacker, Paul Posluszny had the third-worst run stop rate in the league last year, while Andra Davis and Akin Ayodele ranked Nos. 6 and 7, respectively. On the defensive line, Dwan Edwards had the sixth-worst run stop percentage, while Spencer Johnson just snuck out of the bottom ten. In the defensive backfield, Donte Whitner ranked among the league's worst, though did make 25 more run stops than any other DB in the league.
Not all was lost, however, as FO also went out of its way to praise - who else? - Kyle Williams.