How can you have more than three strikeouts in an inning?

Answer 1

In Baseball, in order for a batter to be called out after the third strike, the catcher must catch the ball without it hitting the ground. If he does not, and there is no runner on first base, or there are two outs, the batter becomes a batter-runner. At this point, in order to make the out, the catcher must either tag the runner, or throw the ball to first for a force-out.

Regardless of the outcome of the play, the pitcher is still awarded a strike-out.

As an illustration, a pitcher can face two batters, and strike them both out. A third batter comes to the plate, receives three strikes against him, but due to an uncaught third strike, reach first. A fourth batter can then come to the plate, strike-out, and thus award the pitcher with his fourth strike-out in the inning.