Throught the first eight games, the 49ers run defense surrendered 193 yards per game, allowing a 100 yard rusher in seven of those games. Over the last three games, the run defense has surrendered 115 yards per game, somewhat inflated by the Patriots game in inclement weather and a 44 yard run by Patriots running back LeGarrette Blount.
I’ve written about the run defense here and here prior to, and during, season.
Although they have still given up 100+ yards through the last three games, there is a noticeable difference both schematically and in personnel.