How do I use the double first base?

From January 1, 2027, first base must be either a double first base or a larger 18-inch-square white base (Rule 1-2-9). With the larger single base, play it like a normal base.

The double base has a white half in fair territory and a colored half in foul territory, split by the foul line. As a batter-runner:

• Use the colored half on a play at first.
• Exception: if a fielder is drawn into foul territory to take the throw on a dropped third strike, use the white half.
• On a walk, or an extra-base hit to the outfield with no chance of a play at first, you may touch either half.
• Once you've reached first, always go back to the white half, including for leads, pickoff attempts and tagging up on a fly ball.

On a force play at first, it's interference if you touch only the white half and collide with the fielder. It's obstruction if the fielder touches only the colored half and collides with you.

A batted ball that hits or bounces over the white half is fair; over the colored half, it's foul.