The Battle of Chojnice (Battle of Conitz) occurred on September 18, 1454 by the town of Poland and the Teutonic Knights during the Thirteen Years' War, it was won by the latter. The Teutonic army had around 9000 cavalry and 6000 infantry under Bernard Szumborski. The Polish army had 16000 cavalry, a few thousand servants (who can and usually were used in battles), a few hundred infantry plus 500 mercenaries and burgers from Gdansk and 2000 mercenaries hired by Prussian Confederacy, all under the command of King Casimir IV, advised by chancellor Jan Koniecpolski and Piotr from Szczekociny.

The Polish commanders were counting that the battle would be traditionally won by the Polish heavy cavalry, not caring much about either artillery or infantry. They hadn't thought that opponent could change their traditional strategy, or that the Teutonic soldiers besieged in Chojnice could be anything more than spectators. Bernard Szumborski however had planned a totally different kind of battle.

At the beginning everything went as expected, following the pattern of many other battles between the Poles and Teutons. The Polish cavalry charged with much success, breaking the Teutonic lines, killing Prince Rudolf of Zagan and even capturing Bernard Szumborski. The Teutonic cavalry tried to break through Polish lines and escape to Chojnice; however infantry grouped at Teutonic wegenburg broke with tradition and offer a very good defense against the mounted troops. Then a sudden sally from Chojnice at the back of the Polish army caused panic. Bernard Szumborski managed to release himself and organised pursuit; hundreds of Poles, including Piotr from Szczekociny, were killed during the rout or drowned in nearby marsh. The Polish King fought on with great personal courage and his knights had to force him to leave the battlefield.

The Polish defeat was complete. 3000 bodies were left at battlefield, 300 knights were captured by Teutons, including three main commanders: Mikolaj Szarlejski, Lukasz Gorka, and Wojciech Kostka from Postupice. The Teutons lost only around 100 men. Bernard Szumborski was however formally a Polish prisoner, since he gave a knight's word.

The battle proved that discipline and improved tactics, combined with a talented commander could win against a larger, but more traditional army. The Poles paid the price for ignoring terrain, infantry and artillery.