Around the turn of the century, there was an unwritten, but arbitrary rule that said you couldn't wear straw hats in New York City past September 15th. Newspapers would warn you about the upcoming date, and if you dared wear a hat past the date, you'd probably get your hat snatched and stomped in front of you.
In 1922, a few youth decided to start this stomping tradition early, on the 13th. They targeted some dock workers that actually fought back instead of letting their hats be stomped. A fight broke out and they even stopped traffic on the Manhattan Bridge before police broke it off.
Despite this, the brawls continued and got worse. Gangs of teens would walk around with large sticks - sometimes even with a nail on the top - looking for people with hats to beat them up. Many people were hospitalized, there were mobs as large as 1000 people who were just looking to stomp on hats!