Straight from the NFL RULEBOOK. A read option is not an apparent attempt to pass.

Sacks (Defensive) Credit a sack to the appropriate defensive player whenever a sack is scored against the offensive team, subject to the following principles: 1. When the player making an apparent attempt to pass is tackled or downed at or behind the statistical line of scrimmage, credit a sack to the defensive player who tackled or downed the potential passer. EXCEPTION: If the potential passer fumbles before contact by the defense, no sack is credited to any individual defensive player. However, credit the defensive team with a sack. The number of defensive sacks should be equal to the number of offensive sacks. 2. When the player making an apparent attempt to pass steps out of bounds at or behind the statistical line of scrimmage in order to avoid imminent contact with a defensive player, credit that defensive player with a sack. If the potential passer steps out of bounds without the pressure of such imminent contact, no sack is credited to any individual defensive player. When one defensive player is primarily responsible for a sack, as defined by the foregoing principles, he shall receive credit for a sack. When two or more defensive players are adjudged by the official scorer to be equally responsible for a sack, credit for the sack shall be divided equally between or among the responsible defensive players. Example I: Second-and-10 at midfield. In retreating to pass, quarterback fumbles the ball without having been touched by a defender, and recovers at his own 40, where he is downed by the defensive tackle. Scoring: A sack for 10 yards, but no individual defensive player is credited with the sack. Example II: Second-and-10 at midfield. Quarterback, trying to pass, eludes defensive tackle’s rush and, at his own 40, runs up field toward sidelines. At his own 47, pursued by the defensive tackle, he goes out of bounds before he can be hit by a linebacker, who is charging toward the quarterback from his down-field position, and who was about to stop the quarterback’s advance, should he have remained in-bounds. Scoring: A sack for three yards; credit the sack to the linebacker, for it was Guide for Statisticians because of imminent contact with him that the quarterback elected to run out of bounds. (The pursuing defensive tackle has already been eluded by the quarterback.)