ChicagoSports.com has a weekly Q&A with former NFL official Jerry Markbreit. Markbreit, the only official to referee four super bowls, and sometimes gets confused by "heads or tails" answered questions like this one from fans:
During the Colts-Chargers game there was a play that had two penalties. One against the chargers for illegal formation and the other against the Colts for illegal contact. The referee stated that "the illegal contact penalaty was waved off because the quarterback was out of the pocket." What gives? It seems that this was incorrectly stated or as I see it, every time a quarterback rolls out the defenders can just tackle the receivers. I know that I'm wrong but I need your help on this play. --G.L. Kirby, Charlottesville, Va.
The rules states that an eligible receiver may be contacted by a defender only to a point five yards beyond the line of scrimmage unless the player who receives the snap demonstrates no further intention to pass the ball, including handing off the ball, pitching the ball, or moving out of the pocket. Within this five-yard zone a defensive player may chuck an eligible receiver in front of him. The defender is allowed to maintain continuous and unbroken contact within the five yard zone so long as the receiver has not moved beyond a point that is even with the defender. The defender may not hold or tackle the eligible receiver. This would constitute defensive holding and is not considered illegal contact. This defensive holding foul is not governed by where it occurs on the field.
You can check out the entire Q&A here