There's been a lot of chatter lately about Patrick Peterson landing himself a nice big contract extension, expected to happen fairly soon, in fact. There's also been some debate as to how good Peterson actually is at playing cornerback.

On the whole the opinion seems to be that he's a very good corner. PFF would agree, with grades of +9.3 and +8.9 in 2012 and 2013, respectively. Still, there's one WR with which Peterson seems to struggle, and I'm sure you can guess this one: Michael Crabtree.

We've all seen the embarrassing performances Crabtree has put on display at Peterson's expense, but I thought I'd recount some of them, both statistically, as well as with the help of PFF's grades. Since Crabtree wasn't fully healthy in 2013, I first went back to 2012 and took a look at the two games the 49ers and Cardinals shared.

In week 8 of 2012, the 49ers traveled to Glendale to face the Cardinals. Patrick Peterson probably wishes he went on a trip of his own. Not only did he allow three catches on three targets to Crabtree, but he also gave up two more receptions on two targets to both Mario Manningham, as well as Delanie Walker.

Crabtree finished with three catches for 34 yards, including 25yds of YAC, and two touchdowns...all in Peterson's coverage. He added another two catches for 38 yards against William Gay in what was a pretty good game for the 49ers wideout.

Fast-forward to week 17 of the 2012 season and this time the Cardinals came to San Francisco for a game. Perhaps Peterson wishes he stayed home that day. In five attempts he gave up four catches for 104 yards (including 36 yards of YAC) and two touchdowns while covering Crabtree.

He did defend a pass attempted for Randy Moss, the only other pass he faced...so there's that.

Back in week 11 of the 2011 season Peterson gave up six catches on eight targets, totaling 116 yards (61 YAC) with a long of 38...and that was just to Crabtree. He also gave up two receptions to Kyle WIlliams for 23 yards.

By the way, the previously mentioned 2013 matchup in week 17? Granted Crabtree was just seven months removed from a ruptured achilles tendon, but he still managed two catches on three targets for 24 yards (including 15 YAC), all in Peterson's coverage. Peterson did not defend any other passes that week.

So what is it about Michael Crabtree that presents such a problem for Patrick Peterson? Just how good is the latter, or does he just seem to play his worst games against the 49ers? Is he worth a Richard Sherman-esque contract extension, or where do you have him rated in terms of NFL CBs?