Baseball is the only major professional team sport that does not have a salary cap. Sure, you can make millions by playing football or basketball, but you won't make nearly as much as you could in baseball. Individual sports like golf can pay a lot, but you have to be good at them. In baseball however, you don't have to be all that good. It is a team sport with a 25 man roster, so all you have to do is develop a niche talent that gets you onto the team. Sure, if you can hit lots of homeruns, you will get paid more, but the minimum wage for major league players is $400,000, and the average league salary is just under $3 million. This is why labor unions are awesome.
Here are some niche skills that can get you into the pros
1. Learn how to throw a baseball 85 mph with you left hand. Lefties are only 10% of the population, and left handed pitchers are unusually successful against most hitters, so you will be a hot commodity. If you are left handed and 12 or 13 years old, you can practice throwing hard every few days, and if you seriously dedicate yourself to it, you probably will get into the 80-90 MPH zone by the time you are 20 or so. This should be enough to get you into college for free, or possibly drafted straight out of high school into the minor leagues. Baseball even has a name for mediocre pitchers who are left-handed: LOOGY. It stands for "Lefthanded One Out GuY." (seriously) A LOOGY is brought into a close game toward the end of the game and given a specific job of pitching to a single batter who is known to struggle against lefties. LOOGYs usually appear in about 70 games per year, for no longer than 5 mins at a time. They make between $400,000 and 5 million per year.
2. Find a way to get short and stocky, and have extremely reliable knees. Then learn to catch baseballs. Catchers are a very rare breed of baseball player. They are not usually expected to be very good hitters, and they don't really have to play the field much. All they are expected to do is squat behind the plate for 3.5 hours everyday without their knees falling off. I'm not sure how being short and stocky became a requirement, but it is. Most catchers who turn out to be very good eventually get the nickname "pudge."
3. Learn how to throw a knuckleball. There are about 7 billion people living in the world. To my knowledge, only one of them knows how to throw a knuckleball. His name is Tim Wakefield, and he has been a successful major league pitcher for 18 years. A knuckleball is any way of throwing a ball that causes it not to spin at all. If you can find a way to do this you will go pro. One of the best parts about throwing the knuckleball is that you don't have to throw it very hard. Throwing hard eventually causes your shoulder to break in half, and usually ends baseball player's careers. However, knuckleball pitchers can play effectively into their late 40s or low 50s.
4. Play for the Pirates or the Royals. In Pittsburgh and Kansas City, actual baseball skills are not a requirement to make the team, so you can just show up with a uniform and a glove. Very few people are willing to play for these teams, so they will appreciate you showing up.