Now, let's spend a little more time talking about judgment calls. Learning the rules is as simple as dedicating the time and attention that are needed to read and memorize the rule book. Being decisive is simply a conditioning mechanism, in that you must train yourself to react in a decisive manner. Judgments are a different beast, altogether. You get better at judgments via experience. With nearly every game that I umpire, something happens that is new and not covered by the rule book. As you manage these situations, you learn from them; and, the next time that (or something similar) happens, you are more prepared.
The problem is that you could spend 50 years of umpiring before experiencing it all; and, by then, you might have lost too much of your eyesight to be effective. Umpires have a very simple and very effective mechanism for speeding this up: They tell each other a lot of stories. Umpires love to find another umpire and tell them about something new that happened in their last game, or repeat a story that they have recently heard from another umpire. Umpires just love to communicate to each other and swap stories. They argue, they suggest alternatives, they recall similar situations. Often, they call in a very senior umpire to lend an opinion (somebody who has umpired for 50 years). They also make use of chat boards and e-mail aliases, asking questions and getting opinions.
Each local league has an Umpire Rules Committee that is led by the league's Head Umpire, and this group makes final decisions on the rulings in question, which they then communicate out. I liken this to an umpire's version of the State Supreme Court. They sometimes ask the Little League Baseball Rules Committee to make a global ruling. I liken this to the U.S. Supreme Court, and it is essentially the highest ruling body available. The net result of all this is that experiences are readily shared, which greatly accelerates the learning curve.
Logistics are worth discussing a bit, too. Baseball games need at least one umpire, the home-plate umpire, who calls the balls and strikes, amongst other duties. Ideally, there are field umpires, who watch for plays at the bases and in the outfield. If two field umpires show up, one handles the left side of the field (third base), and one handles the right side (first base). They communicate who handles calls at second base, depending on scenarios into which I won't go. The goal is to have umpires who are in positions to make good calls by being able to see the play clearly, with unobstructed vision, from a close proximity.
Note The closer that you are to a play, the easier it is to see the details. You can see if the fielder has his foot on the base or is not on the base by a fraction of an inch; but you must use your ears to listen to when the fielder catches the ball, to know if the ball gets caught before the runner reaches the base. This all happens very quickly, and it involves developing skills with multiple sensors.
Together, the home-plate and field umpires are referred to as the umpiring crew. During the game, the members of the umpiring crew help each other. If one umpire gets in the wrong position, that umpire might ask the others to huddle up to decide a call. Also, if there is a ruling in question, the umpires will often get together to ensure that they are recalling the rule correctly.
Sometimes, this involves a judgment call, and one of the umpires has experience with or has learned about a similar ruling to be applied. The crew works as a team, with the home-plate umpire being the lead umpire (who has final say). The league makes sure to schedule umpiring crews so as to ensure that they have at least one experienced umpire in the game. Often, this is the home-plate umpire.
With little league, it has been my experience that sometimes only one umpire shows up for the game. This person must become the home-plate umpire; from there, this person must make all of the calls, albeit from a difficult perspective on some faraway plays. I have learned some interesting umpire math, too. Sometimes, 1 + 1 = 0. Let me explain.
I was alone for a game, so that both teams volunteered a parent to umpire in the field. I was pleased, because now I had what I thought were two field umpires, which should have made the game easier to manage. As the game progressed (and I began to realize how inexperienced these umpires were and what a difficult situation I was having, trying to fix mistakes), I recognized that I would have been better off doing the game alone. "1+1 = 0" means that adding a couple of inexperienced umpires will not help productivity. I daresay that, on occasion, 1+1 = -1, and that it causes more harm than good.