I've never seen anything like it at a gig before.
Frank Turner was nearing the end of a triumphant hour-and-a-half set at Lincoln's Engine Shed with the second to last song in his encore, the fan favourite Photosynthesis.
Like many of Turner's best-loved songs, it's a rising call to arms celebrating youth, immortality and the freedom to make mistakes with the affable chorus: "I won't sit down and I won't shut up, but most of all I will not grow up".
But towards the end of the song, without any instruction or request from Turner, an 1,800-strong sell out crowd took to the ground and sat down, en masse.
You see, it's a popular tradition at a Frank Turner gig when he plays this particular song.
The idea is that hundreds of bodies jump right into the air when the drums kick in for the final refrain.
And the idea of hundreds of music fans simultaneously performing the same action almost telepathically is a testament to how beloved Turner really is.
"It's amazing that a couple of thousand people can come together and leave their differences at the door and just treat each other as friends and equals," Turner said from the stage, visibly overwhelmed by this show of unity from fans both young and old.
Turner's Engine Shed gig rounded off an incredible year which has seen him release one of his most critically-acclaimed albums, sell out Wembley Arena and even play to more than 28 million people at the Olympics opening ceremony.
Since splitting from Million Dead and going solo in 2005, Turner has played more than 1,000 live shows, so to say it's what he does best would be an understatement.
I can do without the occasional anti-Bono protest folk, like the atheist anthem Glory Hallelujah, which perpetuates Turner's utopia of unity by telling us there's no heaven, hell and that we're only in it for ourselves. But even when he's at his most preachy, he still does it with a sense of charm and melody which makes it difficult to stay annoyed.
But perhaps his biggest attribute is the way he makes every word and every note of his songs believable.
Whether it's older material like I Knew Prufrock Before He Got Famous and Long Live The Queen, or newer songs such as Wessex Boy and I Still Believe, Turner tells a vivid story which fans take to their hearts.