Uncaught third strike
In baseball and softball, an uncaught third strike (sometimes referred to as dropped third strike) occurs when the catcher fails to cleanly catch a pitch for the third strike. A pitch is considered uncaught if the ball touches the ground before being caught (a bouncing ball), or if the ball is dropped after being grasped (see also catch). In Major League Baseball, the specific rules concerning the uncaught third strike are addressed in Rules 6.05 and 6.09 of the Official Baseball Rules.
On an uncaught third strike with no runner on first base or with two outs, the batter immediately becomes a runner. The strike is called, but the umpire does not call the batter out. The umpire may also actively signal that there is "no catch" of the pitch. The batter may then attempt to reach first base and must be tagged or thrown out. With two outs and the bases loaded, the catcher who fails to catch the third strike may, upon picking up the ball, step on home plate for a force-out or make a throw to any other fielder.
One intent of this rule is to ensure that a defensive player fields the ball cleanly in order for that team to record an out. It was thought that it was not enough that the offensive player be unsuccessful at the plate in order for an out to be made; a defensive player must be successful as well.
Regardless of the outcome of an uncaught third strike, the pitcher is statistically credited with a strikeout. Because of the uncaught third strike rule, it is possible for a pitcher to register more than three strikeouts in an inning, a feat which has been accomplished in Major League Baseball 67 times. The last time there were four strikeouts in a single inning was in the bottom of the 1st inning during a game between the Boston Red Sox and the Detroit Tigers on October 12, 2013 with Anibal Sanchez pitching for the Tigers and Shane Victorino of the Red Sox reaching 1st base after swinging for strike 3 on a wild pitch.
If at the time of the strike three pitch, first base is occupied with fewer than two outs, the batter is automatically out and cannot become a runner. This is to prevent the defense from deliberately dropping a third strike pitch and getting a double or triple play as a result, because of the possible force play at second, third base, or home plate in this situation.
In Little League, in the Tee-Ball and Minor League divisions the batter is out after the third strike regardless of whether the pitched ball is caught cleanly by the catcher. In Little League (or the Major Division), Junior, Senior, and Big League divisions a batter may attempt to advance to first base on an uncaught third strike. Little League Major Division Softball as well as many other youth baseball leagues, such as the USSSA also follow the rule.
Following a controversial play involving this rule in the ninth inning of Game 2 of the 2005 American League Championship Series, the application of the rule was changed when a comment was added in 2006 to Rule 6.09(b):
"Rule 6.09(b) Comment: A batter who does not realize his situation on a third strike not caught, and who is not in the process of running to first base, shall be declared out once he leaves the dirt circle surrounding home plate."
This comment represents the official interpretation of the application of the rule. Prior to this rule change, a batter was able to try for first at any time before entering the dugout.
On May 17, 2011, Miguel Cairo advanced to first after leaving the dirt circle when the umpires failed to enforce Rule 6.09(b). 
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