- Whenever there are two outs
- When there are less than two outs with first base unoccupied (at the time of the pitch)
Pitches that hit the dirt and are then caught by the catcher are still considered to be "dropped" third strikes. In the event of a dropped third strike, the hitter should run hard towards first base while staying on the right side of the foul line. If the batter is on the foul line (or anywhere to the left of it in fair territory), he places himself at risk of an interference (out) call should he get hit by a throw down the line.
This rule is designed to protect the offense against easy double plays. If it were not for the rule (and batters were always eligible to advance on dropped third strikes), catchers would intentionally drop the third strike and then fire the ball down to second for the force out---which could then result in a double play on a subsequent throw to first base.
So, anytime the easy double play scenario exists (less than two outs with a runner on first), the hitter is out immediately on the third strike, whether it was dropped or not.
