30 000 Serb knights in the battle of Kosovo field of blackbirds, try to defend against 70 000 invading ISLAM army from the Ottoman empire under the leadership of Sultan Murad I. . Serb army led by Prince Lazar Hrebeljanović, The army under Prince Lazar consisted of his own troops, a contingent led by Serbian nobleman Vuk Branković, and a contingent sent from Bosnia by King Tvrtko I, commanded by Vlatko Vuković. Prince Lazar was the ruler of Moravian Serbia, and the most powerful among the Serbian regional lords of the time, while Vuk Branković ruled a part of Kosovo and other areas, recognizing Lazar as his overlord.. The Battle of Kosovo took place in the Kosovo Field, about 5 kilometers northwest of modern-day Pristina.
The bulk of both armies were wiped out in the battle; both Lazar and Murad lost their lives, and the remnants of their armies eventually retreated from the battlefield. Since te Ottomans were the Invading army and had to retreat to Turkey, I consider this battle a win for the Serbs. However the Serbs were left with too few men to defend their lands effectively, while the Turks had many more troops in the east. Consequently, the Serbian principalities that were not already Ottoman vassals, one after the other became so in the following years.
Serbian Despotate would, on numerous occasions, attempt to defeat the Ottomans in conjunction with the Hungarians until its final defeat in 1459 and again in 1540 when Serbia and Serbian lands became ockupied.