Cutting your toenail too short or rounding the edge of the nail can cause it to grow into the skin. Wearing shoes or socks that don't fit well can also cause an ingrown toenail. If your shoes are too tight, they might press the nail into the toe and cause it to grow into the skin. You can get an ingrown toenail if you hurt your toe, such as stubbing it. This can cause the nail to grow inward.
However, jockeys tend to be shorter than normal to meet the weight guidelines. The average height for a jockey is between 4 feet 10 inches and 5 feet 6 inches.
Jockeys tend to be short people only because they can make the weight assignments required in thoroughbred horse racing. I am 5' but I was one of the shorter jockeys. The average jockey is somewhere between 5'2 and 5'4.