Here's a nod to the only Isebrand written history knows. On this day in 1500, Wulf Isebrand, a Dutch transplant to the proto-republic and effectively autonomous district of Dithmarschen, Germany, led the district's militia in a successful defense against superior numbers of Danish and Kalmar Union royal forces, as well as mercenaries, at the Battle of Hemmingstedt.
And that's about the whole story. It can be told in one long sentence.
To be sure, there are additional details about the battle in several sources, mostly German ones, so I can't obtain them easily and if I did, I couldn't read them.
Below are some details I've gleaned from online secondary sources and one email exchange with a very patient historian. There's this article about the Battle of Hemmingstedt, but it's woefully bereft of citations or even proper attribution. Another article in German is available on the Dithmarschen Wiki website.
By opening the sluices of at least one dike, the Dithmarschers flooded the fields either side of a main road across which they also built up a barricaded mound as the focus of their defense.
By denying the Danes, nearly half of whom where mounted and in full armor, the ability to form a broad line of attack or to outflank them, the Dithmarschers negated not only the Danes’ numerical superiority but the offensive advantage mounted cavalry can bring to a battle.
This defense meant the Danes were forced to advance in a sort of funneling approach, making them a much easier target and, with deadly consequences, eliminating any route for effective retreat. If there were areas of exposed land amid the flooded fields, heights between the fields' flooded ditches, I presume they were not in a means of effective approach for the attackers, though they may have been means for maneuverability during counterattack by the Dithmarschers, for sources tell of the defenders using long poles to vault over the waters!
A large number of invaders died by drowning. Even if the water was only a couple of feet keep, it could be a death sentence for armored soldiers and cavalrymen. The weight of a Dane’s armor and the way it compromises maneuverability would have disadvantaged him and made him vulnerable while fighting in the water, but it would have destined him to drowning if he actually fell into any water that was deep enough—and apparently much of it was.
When it came time to retreat, mostly if not entirely back along the same road on which they'd approached and which was congested with others trying to advance toward the engagement, the Danes and mercenaries, would have been basically trapped. (Depending on the source one reads, the mercenaries were Dutch or German and were called the Great Guard or the Black Guard.)
The retreat quickly became a humiliating rout, and Wulf Isebrand a local hero.
Thousands of attackers died, and the Dithmarschers captured the Dannebrog, the flag of the Danish kings—its famous design dating back to at least the mid-1300s and which is used as the flag of Denmark to this day.
Wulf married a local woman and lived out his days in Dithmarschen.
Image, top: A 1910 painting by Max Friedrich Koch depicting the battle. The painting is in the assembly hall of the former District Building in Meldorf, Schleswig-Holstein, Germany.
Image, middle: The logo of the Wulf Isebrand Schule, a primary school in Albersdorf, Schleswig-Holstein, Germany.
Image, bottom: A brick-relief stylized likeness of Wulf Isebrand on a northeast-facing exterior wall of the Wulf Isebrand Schule in Albersdorf.