Shin guards have been used in soccer as early as the 1800s, when players would wear them under thick wool socks. By the 1950s and 1960s, however, shin guards had fallen out of favor with soccer players as the game became more refined and less rough. At the time, there were no rules requiring players to wear shin guards. It was not until 1990 that FIFA made shin guards a required part of the player's equipment.
FIFA's laws of the game specify that shin guards must be made of "rubber, plastic or a similar suitable material." What is considered a "similar suitable material" is left to discretion of the referee, who must decide if the equipment poses a risk either to the player wearing it or any other players on the field. The shin guards must also provide a "reasonable degree of protection" in the opinion of the referee.
A player's shin guards must be worn under his socks, so that they are completely covered. Soccer players wear tall socks that come up to the point just below the knee, meaning that shin guards can cover up to that point. If a player's socks come down during the game, revealing his shin guards, the referee will ask him to pull his socks back up.
All players' equipment, including shin guards, must be inspected by the referee and his assistants before the game. They will check to see that all the players are wearing shin guards and that they are safe. If a player's shin guards come off or become defective during the game, the referee can send the player off, without stopping the play. The player can return to the field once they have been fixed and the referee or one of his assistants has inspected them.