How do I use the double base at first?

Every USA Softball division uses a double first base: a white half in fair territory and a contrasting-color half in foul territory (Rule 8, Section 2N).

• Running to first when a play is being made on you: touch the colored (foul) half. The fielder uses the white half.
• If you touch only the white half on that play, you can be called out on appeal, unless you get back to either half before the appeal.
• If you touch only the white half and collide with a fielder there who's about to catch the throw, you're out for interference.
• On a throw from the foul side, or a bad throw that pulls the fielder into foul ground, either of you can use either half.
• When there's no play on you (for example, a ball hit to the outfield), you can touch either half.
• Once you're on first, you can use either half, including when tagging up on a fly ball.

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