[APG]

NFL Rule Book (2011)
Rule 8, Section 3

Article 1 Legal and Illegal Acts. On a scrimmage play during which a legal forward pass is thrown, an ineligible offensive player, including a T-formation quarterback, is not permitted to move more than one yard beyond the line of scrimmage before the pass has been thrown.

Item 1: Legally Downfield. An ineligible player is not illegally downfield if, after initiating contact with an opponent within one yard of the line of scrimmage during his initial charge:

(a) he moves more than one yard beyond the line while legally blocking or being blocked by an opponent; or
(b) after breaking legal contact with an opponent more than one yard beyond the line of scrimmage, he remains stationary until a forward pass is thrown; or
(c) after losing legal contact with an opponent more than one yard beyond the line of scrimmage, he is forced behind the line of scrimmage by an opponent, at which time he is again subject to normal blocking restrictions for an ineligible offensive player.

Note 1: If an offensive player moves beyond the line while legally blocking or being blocked by an opponent, an eligible offensive player may catch a pass between them and the line of scrimmage.

Item 2: Illegally Downfield. An ineligible offensive player is illegally downfield if:

(a) he moves more than one yard beyond the line of scrimmage without contacting an opponent; or
(b) after losing contact with an opponent within one yard of the line of scrimmage, he advances more than one yard beyond the line of scrimmage; or
(c) after losing contact with an opponent more than one yard beyond the line of scrimmage, he continues to move in any direction.

Penalty: For ineligible offensive player downfield: Loss of five yards from the previous spot.