In the 20 years Brendan Ekstrom, a guitarist for American rock band Circa Survive, has been performing, he has never walked off stage mid-song.
But that all changed earlier this week, when the 39-year-old saw something in the audience of a St. Louis show that was so disturbing that he felt forced to leave.
The guitarist posted a series of messages to his fans on Twitter to explain why he “mysteriously disappeared” halfway through a song.
"Quick note to those who were at the show last night," he wrote to his followers. "I've been doing this for 20 years and I've never walked off stage during a song before.
"For almost a whole song I watched a guy stand a row behind a girl flirting and then trying to kiss her."
Ekstrom explained that as he watched the pair, he became confused as to what was happening.
"At times she seemed OK with his advances but after the second time of watching her push his face and hands away and try to turn...back to watch the show, I asked the security guard to go check on them."
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When the security guard was unclear about what he was asking, the musician felt he had no choice but to confront the man himself.
"I left the stage and walked straight for them, my mind an emotional blur," he wrote. "The man seemed dumbfounded when I showed up...as if nothing was wrong."