When it is legal for a defensive player to interfere with an eligible receiver once the ball is in the air? Many of you asked that question this week after referee Walt Anderson overturned a pass interference penalty on the Dallas Cowboys during the Chicago Bears' 34-18 victory.

Anderson's crew initially flagged Cowboys cornerback Brandon Carr for interference on Bears receiver Brandon Marshall, a third-down penalty in the end zone that would have set up the Bears with first-and-goal. Cowboys coach Jason Garrett challenged the call, noting that safety Darren McCray -- who was about two yards inside the end zone -- tipped the pass before it reached Marshall and Carr in the back of the end zone.

The rule in these situations seems clear. According to NFL Rule 8, Section 5, Article 1: "Defensive pass interference rules apply from the time the ball is thrown until the ball is touched." Therefore, any contact that occurs after it is touched -- i.e., McCray's tip -- is legal. A case example provided includes this assertion: "Interference rules ended when defensive player touched the pass."

But what happens when the contact occurs before the tip? A closer look at the replay indicates that's what happened. Carr had his left hand on Marshall's back and then used it to grab the front of Marshall's jersey. He also used his right arm to pin Marshall's left arm before Marshall dove for the ball. If interference rules end when a defensive player touches the pass, doesn't that mean they are still enforced before that point?

That's what I thought, as did longtime NFL executive Mike Perreira, who was analyzing the game on Twitter. Pereira examined the play several times and concluded: "the interference clearly occurred before the tip." But when Anderson announced the reversal, he said the ball was tipped "prior to the pass interference." The pass was ruled incomplete, and the Bears were left to attempt a field goal on fourth down instead of getting a first-and-goal.

Pereira acknowledged he was surprised by the decision. There are only two explanations here: Anderson couldn't find irrefutable evidence that the tip occurred before the contact, or he simply made a mistake. The number of camera angles available on Monday night makes the first possibility highly unlikely.

Now on to our weekly Penalty Tracker: