Bernie Ecclestone's Formula 1 is the richest sport. Mainly because of the amount of money that sponsors put into the sport, it means that the drivers get paid a vast amount of money, and the cost of making the racing cars isn't cheap.
Soccer is a close second as the richest sport. The major reason for this being that it is the most commonly played sport worldwide. It is the most popular sport among different societies, because of the ease of understanding the rules, and the most basic equipment isn't hard to come by. Some sports are restricted to certain countries because of the cost associated with the up-keep of the equipment and the training.
Golf is also very rich, mainly because of the cash prizes that are awarded upon the winning of major championships, and the funding through the sponsors. There are also cash bonuses based on each individual golfers' contracts.
The NBA is also a rich sport, purely because of the the amount of money in circulation regarding the salaries of the athletes involved. The NBA employs players that have traded between teams, and negotiated contracts, that are some of the most expensive contracts across any sporting body.
- The Money Invested into a Sport
From another perspective, there is a lot of money invested in horse racing. It normally requires a vast amount of money to be even actively involved in horse racing, so the amount of stagnant money that is involved with horse racing is probably more than the cash involved with Formula 1. However, it is the amount of money that is actively invested in the sport.