When can the batter run on an uncaught third strike in Majors?

The uncaught third strike applies in the Major Division. The batter becomes a runner when strike three isn't caught and:

• first base is unoccupied, or
• first base is occupied with two outs.

The defense retires the batter-runner by tagging them or first base before they reach it. To call a batter out for abandoning the effort, they must step into dead ball territory; starting toward the dugout isn't enough.

With first base occupied and fewer than two outs, the batter is out. If that batter runs anyway and draws a throw, it isn't interference, but announce clearly that the batter is out.

If the uncaught strike goes into a dead ball area, the batter-runner is awarded first base only.