Many people believe the name comes from the sport of boxing. Nope. That's a delightful, wrong guess. If that were true, we’d also call the day after Thanksgiving “Turkey Punch Day.”
The real answer involves servants, churches, and a lot of leftover generosity. It’s a tale of Victorian-era bosses being forced to be nice for exactly one day. Imagine your worst boss, but wearing a top hat and handing you a ham.