The historical reality of this battle is is a matter of conjecture, with little evidence for any of the details. Most historians believe that tellings that have survived do refer to a clash between Ottoman invaders and Slavic peoples already in the area.
The Ruling Knez (Prince) of Serbia, Lazar Hrebeljanovic, was given a powerful ultimatum. He was given the choice to surrender and step down or fight and die by the invading Ottomans under Sultan Murad I. Lazar Hrebeljanovic chose to fight and raised an army amounting to about one half of the total Turkish force, which gathered not just a Serb army but a real Balkan coalition. He received help from his neighbouring countries, most notably from Albanians and Hungarians, and even had a contingent of mercenaries made up mostly of Saxons (Germans).
The army marched out to meet the Turks at the so-called "field of blackbirds" or Kosovo Polje. The battle started with Serbian noble and Lazar's son-in-laws General Vuk Brankovic on one wing, Lazar in the center, and Captain Milosh Obilich (a.k.a. Millosh Kopili) and Lord Ivan Kosanchich commanding the third wing of the Christian army.
Opposite the Christians, Sultan Murad I led his Turkish army of over twice the Balkan army's size. The two armies clashed and the Turks immediately gained the upper hand because of their numbers. But, as the day progressed, it seemed the Christians were gaining a tactical advantage. The two wings pushed forward and each side made their way into the Turkish camp. But, the center army under Tsar Lazar was being stopped. This army was being beaten so badly that Lazar was caught in the melee and then, after being enslaved, was slain in front of Sultan Murad I. Upon knowledge of this, Vuk Brankovic retired from the field with his 12,000 knights, betraying his King and his people. The other two armies were also beaten, giving a way to the Turks to proclaim a clean victory.
During the battle Captain Milosh Obilich (thought to be of Albanian descent) went into the tent of Sultan Murad I, posing as a traitor and offering his knights and his loyalty. As he pledged allegiance, he stood up and stabbed Murad I with a poisoned dagger. Murad I died and Milosh Obilich was killed trying to escape the camp. This marked the Turkish army's victory and centuries-long occupation of the Balkans.