What’s the deal with playing the national anthem before sporting events?

The biggest music story in America this week has to be the continuing kerfuffle around NFL players taking a knee during “The Star-Spangled Banner” at the start of games. It’s now NFL policy that players who want to protest do it in the locker room or somewhere off the field. If any player breaks the rule, the team will be fined.

While most team owners have agreed to go along with the new rules, several have said they will take the fine hit because they believe their players have the right to express their opinion over police shootings of unarmed black people.

But let’s back up. Why is the national anthem played before a sporting event, anyway? What’s so special about those occasions? CNN takes a look at the situation in America.

Here’s a fascinating fact: The national anthem was played at baseball games decades before it was actually the national anthem. There are records of “The Star Spangled Banner” gracing the diamond going back as far as 1897, but the song wasn’t adopted as the national anthem until 1931.

Over time, a mix of technology, war, and keeping up appearances kept the song in the sports spotlight. Its first big moment reportedly came in 1918 during the 7th-inning stretch of the World Series.

It’s no coincidence that its first surge in popularity came during wartime. Nationalism stoked by World War I meant that people were more affected by the song, and the fact that major league baseball players were being actively drafted meant those who weren’t drafted benefited from showing their patriotism. Over time, other sports began adopting the practice.

Historian Marc Ferris wrote a history of the national anthem in which he points out that, at first, the anthem didn’t exactly come free.

“The thing is, you had to hire a band,” he told NPR in 2016. “That was expensive, so it was only for special occasions,” like opening day.

Ferris says that after World War II, sound systems allowed teams and parks to play the anthem sans band. That’s when the practice became particularly widespread, because the new tech coincided with a huge swell in patriotism. Understanding the etiquette in sports game national anthems will help us to better analyze the why this patriotism has been so pervasive.