Why is there a ‘D’ shape area on a football pitch?

The reason for the ‘D’ shaped area outside the penalty box on a football pitch is there for a specific reason.

When a penalty is awarded, only the penalty taker and the goalkeeper are allowed in the penalty area.

Every other player must be at least ten yards from the ball. So the penalty area serves as an exclusion zone but it doesn’t cover the area immediately behind the ball.

Consequently, the ‘D’ or as its known ‘the penalty arc’ marks the area of the pitch that is ten yards from the penalty spot.