What are the "9-yard" marks on a football field?

The correct answer identifies the "9-yard" marks as the markings 9 yards from the sideline. These marks are used primarily for establishing the boundaries for plays and are strategically placed to assist players, coaches, and referees in assessing the field position during the game.

The significance of these markings lies in their utility for observing potential plays and ensuring that players remain within the limits of the playing field. They help define the available space for a team to execute plays without risking out-of-bounds situations.

Other options focus on different aspects of the game. For instance, markings 9 yards from the goal line would refer to specific spots for offensive plays but don’t directly relate to the general use of sideline distance markers. Similarly, markings for extra points and penalties pertain to particular game scenarios rather than the general field layout and its use during gameplay. Therefore, the recognition of the "9-yard" marks as those situated 9 yards from the sideline is essential for understanding their practical application on the field.