Hoping players can police low hits

There is a fundamental difference between the two high-profile low hits we've seen this preseason, and together they illustrate the NFL's complicated path in overhauling legal contact between opposing players.

Earlier this month, Miami Dolphins tight end Dustin Keller suffered a career-threatening knee injury after a low hit by Houston Texans safety D.J. Swearinger. Afterward, Swearinger said he struck Keller's knee because of the NFL's updated rules on hits to the head.

Minnesota Vikings defensive tackle Kevin Williams hyperextended his knee Sunday night when San Francisco 49ers offensive lineman Joe Looney went low on a peel-back block. The NFL has not commented on the play, and as colleague Mike Sando wrote, it didn't appear to violate league rules as currently written.

The NFL's competition committee could propose next winter to ban all direct hits to the knee, as NFL operations chief Ray Anderson told The Associated Press. But typically such changes are based on data that suggest a growing trend, and only one of these two hits would apply.

Head-to-head contact is not a problem in blocks, so Looney's hit can't be viewed as a reaction to the league's updated rules. Perhaps it was uncalled for, but it will be an outlier in any study on low hits this season.

In order for the NFL to take measures against low hits, it will need to see a sizable uptick in plays like the one Swearinger made. Frankly, the devastating nature of Keller's injury -- he tore three ligaments and dislocated his kneecap -- likely has built an unofficial boundary around direct knee shots. At least I hope it has.

Otherwise, the league will be left to further limit legal contact, a tricky task to say the least. Chicago Bears linebacker Lance Briggs recently joked that the legal contact area for a ball carrier is now the navel and below. If the league takes action on direct hits to the knee, it'll be much smaller. In this case, you hope players can police themselves.