As part of the ongoing trading and territorial disputes between the Hanseatic League, Sweden, and Denmark, the Hanseatic cities made an agreement with Sweden and Holstein to jointly attack Denmark, the agreed targets being Helsingborg and Copenhagen. The Mayor of Lübeck, Johann Wittenborg, was put in command of an attack force of some 3,000 men,[1] and 50 small seagoing ships, 5 of which had been paid for by Magnus Eriksson, King of Sweden.
As Wittenborg's fleet sailed through the narrow Øresund en route to Copenhagen, he was persuaded to attack the town of Helsingborg and its fortified citadel. He disembarked his fighting men and besieged the stronghold for several weeks. Meanwhile, Valdemar Atterdag, King of Denmark, assembled his fleet capable of carrying an army of 2,500 men and made a surprise attack on the Hanseatic Fleet.
The Danish were victorious, as most of Wittenborg's soldiers were in the town. The Hanseatic cities lost twelve of their ships and several of their nobles were captured.