From BR Bullpen
An out is an event which puts an end to a batter's turn at the plate or to a baserunner's presence on the bases. Once three outs have been recorded, the half-inning is over and the fielding team becomes the batting team, and vice-versa.
 Types of out
 Batting outs
 Baserunning outs
A baserunner is out when the ball catches him away from the base he can safely occupy. This can happen in a number of ways:
- a runner can be picked off if he is tagged with the ball while not in contact with the base he is occupying; this typically happens when the runner has taken a lead from his base (i.e. has moved away from the base in the direction of the next base he is trying to reach) and the pitcher throws to the base he should be occupying before the runner can return there. A runner can also be picked off a base by the catcher.
- a runner can also be out trying to steal the next base, or trying to advance on a potential wild pitch or passed ball, if the ball is relayed to the base he is trying to reach before he arrives and he is tagged while not in contact with the base.
- a runner is also out if he attempts to advance to the next base on a batted ball and the fielders succeed in relaying the ball to that base before he arrives. The play may be a force out or may require a tag, depending on the situation. This also applies to the batter if he tries unsuccessfully to advance an extra base on a base hit.
- a runner is out if he fails to return to his base when a batted ball is caught on the fly, or leaves his base before the ball is caught while advancing to the next base (in this case, the out is made as the result of an appeal).
- a runner is out if he violates one of the three cardinal rules of baserunning: he fails to touch a base; he passes another runner; or he reaches a base that is already occupied.
- a runner is out if he commits interference, willfully or not. For example, he is out if hit by a batted ball in fair territory, or if he interferes with a fielder trying to field a batted ball or a throw, or if he runs out of the basepath to avoid a tag or disrupt a fielding play such as an attempted double play.
 Other outs
A player can also be called out for making a mockery of the game, or for abandoning his effort to reach a base he is entitled to. For example, a batter who draws a walk but returns to the dugout thinking he has struck out will be called out once he leaves the field of play.
 Fourth out
While an inning normally ends after three outs have been recorded, there are some rare cases when a so-called fourth or even a fifth out must be recorded by the fielding team to prevent runs from being scored. This can best be explained by way of an example:
- With the bases loaded and one out, the batter hits a fly ball to deep right field. The baserunners expect the ball to fall for a base hit and are all running on the play. However, the right fielder makes a terrific play and catches the ball for the second out, then relays it to first base to put out the runner from first base who has not had time to return to his base. This is the third out, and the inning is over; however, if the runners from second and third base have already crossed the plate before the third out is recorded, their runs count, even though they have left their bases early. Therefore, the fielders must also tag second base and third base in order to "put out" those two runners and erase their runs from the scoreboard. In this case, no putout or assist is granted to the defensive players recording these two extra outs, but they are still required. In this case, the two baserunners cannot attempt to return to the bases they left early, since the inning is already over, and as soon as they touch third base in trying to retrace their steps, the run they had potentially scored is wiped off.