Major Rule Changes for 1940
On January 11, 1940 The rule requiring players removed for substitutes be ineligible for return until a subsequent quarter, with the exception of two permitted returning players in the fourth quarter, remained unchanged.
Other important changes were enacted by the NFL for its 1940 season, however. These included:
The penalty for clipping was reduced from 25 yards[6] to 15 yards.
A penalty committed in the field of play could no longer carry the ball more than half the distance to the offender’s goal line.
For offensive pass interference committed in the end zone, the defense now had the option of placing the ball 15 yards from the previous spot with a loss of down, or taking the ball on the 20 yard line via touchback.
Penalties for fouls that occur prior to a pass or kick from behind the line of scrimmage were to be enforced from the previous spot. However, penalties for fouls during a free ball or when the offensive team fouls behind their line were to be enforced from the spot of the foul