http://www.si.com/nfl/2015/06/19/evan-m ... chip-kelly
This is a pretty interesting article about Mathis. The writer first notes that, over the last four seasons, Mathis have been ranked first, first, first and second in the PFF guard rankings. He was downgraded only once every 16.4 snaps as a run blocker.
The writer then begins "digging for negative plays for this piece." He wants to "see if [this anecdotal evidence] indicates a larger problem." The thing that makes the article somewhat interesting is the fact that Mathis gives his own response to these plays.
One of the plays was against the Seahawks:
Mathis: "It’s fourth-and-1, so I’m trying to get my head inside and get a strong initial push. He’s able to shed me and get the assist, but he didn’t get any penetration and has no upfield momentum. Now we’re first-and-goal on the 3.
Mathis gets a good initial push on Tony McDaniel, driving him passed the LOS, but McDaniel uses his power to knock Mathis off balance, keeps his eyes on the backfield, and gets to McCoy for the assist. Williams also did an admirable job on this play, driving into the backfield and splitting two double teams to make a pile. K.J. Wright does not read the back well and bites down hard. Chancellor seems to hesitate and looks a step too late on this play. If he had stepped toward McCoy with his right leg to maintain inside leverage, he might have cut him off and prevented the first down. I guess that's easier said than done against a shifty back like McCoy.
The fact that the writer was digging for dirt, and this was one of the worst plays he could come with, is fairly telling.