As in, "I tripped over my shoelace and took a header."
The word took on its modern meaning when the high-wheeled bicycle came onto the scene. The high-wheeler seating position puts the rider above the big front wheel, almost on top of the drive axle. This puts the rider's center of gravity high, and forward, on the bike. When something stops the front wheel, even momentarily, the mass of the rider shifts forward and...down. Down in a darn quick hurry, too.
Because the handlebar of the bike is basically situated across the rider's lap, there is no way for the poor unfortunate soul to get away from the machine as it tilts forward. The bike becomes a hammer, and the rider is a nail, driven head-first into the ground.
Thus, the origin of the term "header".
I have taken exactly one header on my high-wheeler, and I truly, truly, hope to never take another. I was only moving at about 2 miles per hour when I crashed, and I really thought I might die, as it was happening.
Brad, Valerie and I had driven from Parker up to a parking lot at Dartmouth and Havana. There, we unloaded the bikes and hit the Cherry Creek Trail, then turned onto the Highline Canal Trail and took it to Tamarac Square Mall. There, we planned on stopping at Starbuck's and having some coffee. It was a little bike ride that we made on a fairly regular basis, back then.
That Starbuck's was on the lower level of the mall, which sat a few feet below the grade of the parking lot. Their patio seating was sunken, and you had to step down one step from the parking lot to the sidewalk, then walk down 3 or 4 steps to the patio, in order to go into the building at the lower level.
I had a habit of riding the high-wheeler around to the entrance to the main floor, where I would drop off the parking lot down to the sidewalk and ride a few feet over to the steps which led down to the patio. There, I would dismount, and roll the bike down the handicapped-access ramp to the seating area.
This particular evening, just as I dropped the front wheel off of the curb, a lady came out of the building, through the main exit, right in my path. Instinctively, I turned the wheel to the left.
The wheel dropped the 6 inches down to the sidewalk and, being turned and angling down, it torqued the handlebars out of my hand and the bike slammed straight down to the right. Of course, I was still on it when it hit the ground.
Luckily, it wasn't the classic header, and I didn't auger into the concrete with my skull. Instead, I landed on the handlebar with my left arm, bending the bar 90 degrees and giving me the most impressive (and painful) bruise I have ever had. My right leg was twisted around at a strange angle, from me trying to get free of the bike on the way down, and I walked with a limp for about a week because I pulled a hip flexor.
All in all, I guess it could have been a lot worse. I could have gone straight over the bars, or I could have landed on the lady who was walking out.
As for her, as I was crashing to the ground on a five-feet tall vintage-style bike, she just kept walking as if nothing was going on. She never even looked around, according to Val.
Apparently, this kind of thing was commonplace for her.