Coats of arms became popular during the age of tournaments. Tournaments, which were reportedly invented by Godfrey de Preuilly in 11th century France, were a training ground for knights. They showed off their skills and gained fame (or infamy) almost like the gladiators of old. A tournament itself was really a series of mounted and armored combats, fought in contest form. Many knights competed but only one could win. The one who did prevail received a prize of some sort be it the daughter of a nobleman or a hefty purse of coin.
The events themselves grew in pomp and pageantry. They were the favorite sport of medieval knights and perhaps the crowds they drew in. By the 14th century, a knight needed a coat of arms to even participate in a tournament. There were several types of tournaments in existence during the Middle Ages, each of which had a different form of combat on the menu. For example, a Joust could be an individual tournament event, taking place between just two knights, or it could be a joust a plaisance in which a series of elimination jousts took place over several days with an overall winner being decided. Each knight would receive three chances to face his opponent before being eliminated.
Of course, there was also a pas d’armes (Passage of Arms) tournament. In this type of event, one knight sent out a proclamation decreeing that he would take on all comers at a specific time and location. Then, there were team events. These were referred to as melees. A melee a pied tournament occurred when knights were on foot whereas a melee a cheval was on horseback.