Rule No. 1 of attending a Major League Baseball game as a fan is that you have to keep your head on a swivel at all times. One poor fan, and her head, paid the price over the weekend for forgetting that non-negotiable.

The fan, Jamie Golla, was sitting in the lower bowl down the third-base side at T-Mobile Park in Seattle for the Mariners’ contest against the San Diego Padres on Friday night. Her friend just so happened to have her phone out to capture a selfie video of the two of them having fun at the ballpark, with San Diego’s Sung-mun Song at the dish to lead off the fifth inning.

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Quickly, and out of nowhere, the moment went from fun to incredibly painful for Golla.

The selfie video shows the exact moment a screaming foul ball caught Golla on the top of the head, and the sound the baseball made as it made contact with her skull is nightmare fuel.

The foul ball off of Song’s bat wasn’t a routine fly ball, either, hence the fact that fans sitting around Golla and her friend weren’t trying to catch it for a souvenir.

It was one of those foul balls where, whether you’re at the ballpark or watching at home, you hold your breath for a moment, hoping that the screamer doesn’t catch a fan. Unfortunately, it did.

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According to the New York Post, Golla was taken to nearby Harborview Medical Center for treatment shortly after the accident.

“I’m feeling a little better than yesterday. My head is still a bit swollen, and I’ve been getting minor headaches here and there, but overall I’m doing okay. I didn’t think this video was going to blow up. I appreciate the people who have been checking up on me,” she told The Post.

Jamie also shared that a member of the Mariners staff followed up and checked on her after the scary moment, and offered her and her friends tickets to return for a future game.

The Mariners were shut out by the Padres on Friday night, 2-0.