Baseball is a complicated sport, with complicated rules, and after more than a century and a half of play, there is really nothing that hasn't been seen before, and there really is a rule for everything.
Take for example, the so-called "fourth-out rule." Most people know that in baseball it is three strikes and you're out, three outs and the inning is over. But in certain, extremely rare cases, it is necessary for a team to get four outs in an inning. The reason is that this becomes necessary in order to adhere to two other rules.
First of all, when a ball is caught on the fly, runners cannot leave their bases until the ball is caught, after which they may attempt to advance at their own risk in what is known as tagging up. If a runner leaves his base too early, he may be put out by the defending team throwing to the base he left too soon.
Second of all, if a runner crosses home plate before the third out of an inning is recorded, his run counts, unless the out was a force out.
The extremely rare situation where these two rules can lead to a fourth out becoming necessary is when a runner is on third base, another runner is on either first or second, there is exactly one out, and the batter hits a line drive which looks like it is going to be a hit but is instead caught on the fly by a fielder.
In this case, it may so happen that the runners, believing the ball will be a clean hit, start to advance before the ball is caught, and the runner on third crosses home plate before the fielder throws back to the base where the other runner started from.
In this case, most baseball fans, and even most baseball players, would assume that the inning is over and that the run did not score, because three outs were recorded, and the runner on third base left illegally before the ball was caught. However, they would be wrong.
This is where the two other rules mentioned above come in. While it is true that the runner on third left his base illegally, he is not considered out until the defending team throws back to third base. Meanwhile, because he crossed the plate before the third out, his run is considered to have scored.
Therefore, the defending team is required to throw to third base and make a "fourth" out in order to prevent that run from counting, in what is known as the "fourth-out rule" (in actual scoring practice, the runner on third takes precedence and is considered to be the third and final out, where as the earlier throw to the other runner's base is not considered an out, so in the end only three outs were recorded).
In well over 20 years of watching baseball, I had never seen an instance of the fourth-out rule coming up at all until yesterday's game between the Dodgers and the Diamondbacks, and sure enough, the rule took the players off guard as well.
In the top of the second inning with the visiting Dodgers at bat and one out, Andre Ethier was at third and Juan Pierre was at second when Dodgers pitcher Randy Wolf hit a lined smash up the middle which was snagged in a very nice play by Diamondbacks pitcher Dan Haren who then whirled and threw to second baseman Felipe Lopez who tagged Pierre as he attempted to scramble back to second in what was apparently an inning-ending double play.
However, Ethier had broken on contact and had crossed home plate before Pierre had been tagged out. Even though Ethier had advanced illegally before the ball was caught, the Diamondbacks players, thinking the inning was over, walked off the field without ever throwing back to third base to record the "fourth" out, and thus when Dodgers manager Joe Torre came out to argue, the umpires correctly awarded Ethier's run to the Dodgers.
While Torre himself had never heard of the rule, and even the umpires at first seemed uncertain about the call, it turned out that Dodgers bench coach Bob Schaefer alerted Torre because he had seen a similar play decades before while coaching in the minor leagues back in 1983.