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How Does the Magic Yellow First-Down Line Work?

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If you attend a Super Bowl party on Sunday, you’ll probably hear at least one casual football viewer ask, “How do they get that yellow first-down line on the field?” While “magic” is a fine answer in its own right, the real explanation is a bit more technologically intense. Let’s have a look at the background and mechanics behind every football fan’s shining beacon, the yellow first-down line.

Like the first-down line, football fans? You owe a tip of your cap to an unlikely source: hockey. According to Allen St. John’s 2009 book The Billion Dollar Game, the first-down line actually emerged from the ashes of one of sports broadcasting’s bigger debacles: the FoxTrax system for hockey, which was designed by a company called Sportvision. FoxTrax – which hockey fans no doubt remember as the much-maligned “technopuck” that debuted in 1996 – employed a system of cameras and sensors around a hockey rink to place a little blue halo around the puck.

FoxTrax wasn't a great fit for NHL broadcasts. Hockey purists hated the intrusion into their game, and casual fans didn’t flock to hockey just because the puck was suddenly easier to follow. However, the system inspired producers to think of new ways to insert computerized images into live sports broadcasts. The idea of using a line to mark the first down in football was a natural extension, and Sportvision debuted its 1st and Ten system during ESPN’s broadcast of a Bengals-Ravens tilt on September 27, 1998. A couple of months later, rival company Princeton Video Image unveiled its Yellow Down Line system during a Steelers-Lions broadcast on CBS. (Sportvision is still kicking, and ESPN acquired all of PVI’s intellectual property in December 2010.)

But How Does It Work?

It takes lots of computers, sensors, and smart technicians. Long before the game starts, technicians make a digital 3-D model of the field, including all of the yard lines. While a football field may look flat to the naked eye, it’s actually subtly curved with a crown in the middle to help rainwater flow away. Each field has its own unique contours, so before the season begins, broadcasters need to get a 3-D model of each stadium’s field.

These models of the field help sidestep the rest of the technological challenges inherent to putting a line on the field. On game day, each camera used in the broadcast contains sensors that record its location, tilt, pan, and zoom and transmit this data to the network’s graphics truck in the stadium’s parking lot. These readings allow the computers in the truck to process exactly where each camera is within the 3-D model and the perspective of each camera. (According to How Stuff Works, the computers recalculate the perspective 30 times per second as the camera moves.)

After they get their hands on all of this information, the folks in the graphics truck know where to put the first-down line, but that’s only part of the task. When you watch games you’ll notice that the first-down line appears to actually be painted on the field; if a player or official crosses the line, he doesn’t turn yellow. Instead, it looks like the player’s cleat is positioned on top of an actual painted line. This effect is fairly straightforward, but it’s difficult to achieve.

To integrate the line onto the field of play, the technicians and their computers put together two separate color palettes before each game. One palette contains the colors – usually greens and browns – that naturally occur on the field’s turf. These colors will automatically be converted into yellow when the line is drawn onto the field. All of the other colors that could show up on the field – things like the players and officials’ uniforms, shoes, and flesh, the ball itself, challenge and penalty flags – go into a separate palette. Colors that appear on this second palette are never converted into yellow when the first-down line is drawn. Thus, if a player’s foot is situated “on” the line, everything around his cleat will turn yellow, but the cleat itself will remain black. According to How Stuff Works, this drawing/colorizing process refreshes sixty times per second.

All this technology—and the people needed to run it—wasn’t cheap at first. It could cost broadcasters anywhere from $25,000 to $30,000 per game to put the yellow line on the field. Sportvision had to deploy a truck and a four-man crew with five racks of equipment. The cost has come down since then, and the process is now less labor intensive. One technician using one or two computers can run the system, according to Sportvision, and some games can even be done without anyone actually at the venue.

Now you can explain it to everyone at your Super Bowl party during one of the less-exciting $4 million commercials.

This post originally appeared in 2011.

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Watch These Surfers Crush Nantucket's 'Slurpee' Waves
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Instead of hunkering down with Netflix and hot chocolate during the East Coast’s recent cold snap, surfers Nick Hayden and Jamie Briard spent the first few days of January 2018 conquering icy waves in Nantucket, Massachusetts. The frothy swells resembled a frozen 7-Eleven Slurpee, so photographer Jonathan Nimerfroh, a friend of the athletes, grabbed his camera to capture the phenomenon, according to deMilked.

The freezing point for salt water is 28.4°F, but undulating ocean waves typically move too much for ice particles to form. At Nantucket’s Nobadeer Beach, however, conditions were just right for a thick layer of frost to form atop the water’s surface for several hours. Some of the slushy crests were even surfable before melting after about three hours, Nimerfroh told Live Science.

This is the second time Nimerfroh has photographed so-called “Slurpee waves." He captured a similar scene on February 27, 2015, telling The New York Times, “I saw these crazy half-frozen waves. Usually on a summer day you can hear the waves crashing, but it was absolutely silent. It was like I had earplugs in my ears.”

Check out Nimerfroh’s video of surfers enjoying the icy swell below.

[h/t deMilked]

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Big Questions
Why Is the University of Georgia's Mascot a Bulldog?
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Daniel Shirey/Getty Images

For licensing purposes and the all-important "aww" factor, collegiate football teams like their mascots—and few are as popular as Uga, the handsome bulldog of University of Georgia fame.

When Herman J. Stegeman took over as head coach in 1920, the team, which had previously been referred to as the Red and Black, became known as the Wildcats. Atlanta Journal sportswriter Morgan Blake took issue with the unoriginal moniker, pointing out that it was already shared by at least two other teams in the south—Kentucky State and Davidson.

"I had hoped that Georgia would adopt some original nickname that would stand out," Blake wrote, adding that, "The 'Georgia Bulldogs' would sound good, because there is a certain dignity about a bulldog as well as ferocity, and the name is not as common as 'Wildcats' and 'Tigers.' Yale is about the only team I recall right now that has the name."

One week after Blake's story ran, Cliff Wheatley of the Atlanta Constitution referred to Georgia as the Bulldogs several times in his recap of the team's tie at Virginia. The new nickname quickly caught on, and it wasn't long before the sidelines began to see a succession of canines offering their moral support. A fan named Warren Coleman took his bulldog, Mr. Angel, to games from 1944 to 1946; another bulldog, Butch, served as a mascot from 1947 to 1950 (before he was tragically shot by police who mistook him for a stray).

The Uga lineage began in 1956, when a dog owner named Cecelia Seiler dressed her bulldog in a children's-sized team jersey and took him to home games. Uga I patrolled the field for a decade before his son, Uga II, took up the mantle. Uga V, who reigned from 1990 to 1999, appeared on the cover of Sports Illustrated. Uga X, the current bulldog in residence, has been rooting for the team since 2015.

In deference to the dog's position, the University of Georgia goes to considerable lengths to make sure Uga is comfortable during the game. His doghouse is air-conditioned for the warmer months and his jerseys are custom-made. When one of the Uga clan passes, they're buried on stadium grounds in a marble vault. Apparently, not even death will prevent a loyal Georgia mascot from showing their support.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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