Anyone who saw it happen will never forget it. In a November 2010 game, Indianapolis Colts receiver Austin Collie lay stricken on the ground, arms involuntarily held in the "fencing response" pose that indicates brain trauma:
Collie was stretchered off, and every football fan watching it felt their stomach churn. It was just one of four concussions he suffered during the 2010 season.
Violent hits to the head, neck and chest happen when linebackers and safeties are flying at you from opposite directions. When your job is to get into the spaces between defenders, you end up between defenders.
As such, when NFL receivers play in the slot, they play with fire.
It wasn't always so. Back in the 1960s, football was much closer to its rugby roots. The battle at the line of scrimmage was most of the war; two wide receivers would fight one-on-one against the cornerbacks on either side.
Sid Gillman, the legendary San Diego Chargers head coach, revolutionized the NFL by stretching the field horizontally and vertically with five "receivers." Often running out of a two-back set with a single tight end, Gillman's offense attacked run-stopping linebackers and safeties with precision passing routes.
Instead of forcing the ball to a star player, Gillman taught his quarterbacks to read coverages and throw to where they knew defenders wouldn't, or couldn't be.
Gillman had an assistant who took these concepts to the next level, literally, with speed: Al Davis.
Decades down the road, the legendary Raiders head coach and owner's obsession with speed would become a caricature, a joke. Many young football fans know Davis only by stereotype: a guy obsessed with the long-bomb passing game, big-armed quarterbacks and receivers with fast 40-yard dash times.
When Davis took over the Raiders, though, he used speedy receivers and Gillman's offensive concepts to stretch opposing defenses in ways never before seen. As Chris Brown of Grantland.com explained, Davis would combine Gillman's timing routes to attack defenses at three different depths in the same area of the field.
Davis invented what he called the "slot" formation, where both receivers would line up on the weak side. He could then use the two receivers and tailback to get to three levels of the defense.
Here's a Davis combination Madden players know still gets yards in chunks today—the outside receiver running a deep square-in, while the slot receiver runs a go route:
This is how Davis's offense was a "vertical" offense: not receivers running all go routes, but route combinations that make the defense defend as much of the length of the field as possible.
It just so happens that the faster those two receivers are, the more of the field that defense has to cover.
Don Coryell, the head coach at San Diego State while Gillman was the head coach of the Chargers, had been studying, using and expanding upon Gillman's concepts.
One of Coryell's assistants at San Diego State, John Madden, joined the Raiders in 1966, when Davis stepped down as head coach to take over as commissioner of the AFL. Madden quickly became the Raiders head coach in 1969 and executed Davis's vision throughout the '70s.
Davis hired another bright young assistant in 1966: a Stanford man named Bill Walsh.
The NFL is known as a "copycat league," but the brutal, physical defenses of the day (including Oakland's own) made it tough to implement advanced passing concepts and timing routes throughout the league. Coaches and players that could teach and execute these ideas were rare.
However, beginning in 1977, the NFL made a series of rule changes that would change all of that forever. First, they limited cornerbacks to one "chuck" of each receiver. Then, in 1978, they implemented the five-yard contact zone. The league also loosened rules on pass-blocking, giving quarterbacks better protection.
Gillman and his assistants and students were finally able to stretch the field, and their success was unprecedented. Gillman's "coaching tree" is awe-inspiring:
In 1978, Coryell worked his way up to his mentor's old position: San Diego Chargers head coach. There, Coryell deployed Gillman's route concepts out of a one-back set, creating the explosive "Air Coryell" offense. Coryell used athletic Hall of Fame tight end Kellen Winslow like a wide receiver, putting him in motion and using him in deep route packages.
More importantly, Coryell also expanded the role of the slot receiver.
With just one running back, Coryell could use Winslow in combination with three wide receivers. Coryell had two big targets in John Jefferson and Wes Chandler, but he also had Hall of Famer Charlie Joiner, and he used all four of them in different combinations.
Joiner was the forerunner of the modern "slot ninja." Standing 5'11" and weighing 188 pounds, Joiner didn't have the height of his teammates. He was explosively quick, ran precise routes, had great hands and was tough enough to absorb hits from linebackers and safeties in the heart of the NFL's steroid era.
Most of all, though, Joiner was smart. Per the Pro Football Hall of Fame, Walsh called Joiner "The most intelligent, the smartest, the most calculating receiver the game has ever known." Together, Joiner and quarterback Dan Fouts picked apart opposing defenses, making the same pre-snap reads and adjustments and catching the ball where the defense couldn't defend.
It shouldn't surprise that Walsh admired Joiner; he exhibited the same blend of toughness, talent and football IQ that Walsh had in Jerry Rice. Rice played on the outside, as the flanker, but Walsh coached all of his receivers to have that slot mentality.
Walsh's offense expanded upon what Gillman and Davis had done while also pulling from his time under legendary Browns head coach Paul Brown. Walsh discovered that short passing routes, timed and executed to perfection, could act like a running game.
Walsh, Rice and the 49ers moved the chains, kept third downs short and wore out defenses with advanced route packages, precision route running and sure hands. When defenses began to soften and tire, Rice would break away for long gains after the catch. Walsh and the 49ers could pound away with the running game—or get vertical.
Throughout the '80s and '90s, Walsh (and his students and successors) shredded defenses; we now know his legacy as "the West Coast offense." Coryell's students and successors spread, too: Ron and Norv Turner, Ernie Zampese and Mike Martz all had great success.
Slot receivers and advanced passing concepts also came into the NFL via the "Run 'n Shoot." Coaches like Mouse Davis and June Jones pioneered four-receiver sets, with a slot receiver on both sides of the line.
Houston Oilers slot receiver Ernest Givins, working in the Shoot under offensive coordinator Kevin Gilbride, was named first-team All-Pro in 1990. Givins told Sports Illustrated in 1991, "There's no defensive coverage in the world that can stop four good wide receivers."
That was true at the time, but defenses adapted.
The dizzying zone blitz developed by then-Cincinnati Bengals defensive coordinator Dick LeBeau made pre-snap reads much harder. Then-Tampa Bay Buccaneers defensive coordinator Monte Kiffin modified the Cover 2 looks used so well by the Steelers of the 1970s into the "Tampa 2."
Kiffin covered the short and intermediate routes with five shallow zones across the middle of the field and used athletic outside linebacker Derrick Brooks to cover athletic tight ends—and suddenly overmatched slot receivers.
Between the Tampa 2 and the zone blitz 3-4, defenses across the NFL moved away from the "stacked boxes" and man coverage that had always dominated football and dropped more players into zones, patrolling the wide-open spaces of the field into which modern offenses were trying to throw.
It's no surprise, then, that a great slot receiver is a game-changer. Wes Welker, Victor Cruz and Collie have become masters of slipping the slimmer creases in between modern defenders and using game-breaking speed to make defenses pay whether they catch it five or 50 yards downfield.
As Brown wrote in another Grantland story, Cruz's success in New York's offense should be no surprise: Kevin Gilbride is drawing up the plays there, and the Run 'n Shoot was the foundation for the Giants' prolific passing offense.
One of the biggest plays of Super Bowl XLVII was slot receiver Jacoby Jones blazing through the vaunted 49ers defense for a 56-yard touchdown, beating them with speed and great route-running ability down the seam and with incredible post-catch moves:
The most important play of Collie's 2012 season, though, was one he wished didn't happen. In Week 3, he ruptured his patellar tendon, cutting his season short with awful injuries for a second year in a row.
These high-speed receivers darting in and out of defensive zones are at the highest risk for high-speed collisions.
As more spread-based four- and five-receiver offensive sets and packages work their way into the NFL, more defenses will employ shifting, multi-set "amoeba" fronts—which sometimes forgo down linemen completely to blanket the field in zone defenders.
When defenders are locked in man coverage, they're engaged at close range with the receiver. When defenders are on the prowl, sprinting from several yards away to meet the receiver at the ball, bad things happen:
It's this reason that the NFL, according to the National Football Post's Dan Pompei, has been mulling the idea of widening the field to CFL dimensions. By giving slot receivers much more space to work with, in theory, there will be far fewer high-velocity hits on defenseless players just trying to make a catch and hold on to the ball.
This strategy might work, or it may make things worse. With so much ground to cover, defenses could be forced into full-time zones, meaning more defenders are doing more sprinting to keep receivers from shredding them across the middle of the field.
In order to stop more horrific injuries like Collie's, though, all options must be on the table.
If nothing changes, slot receivers will replace running backs as the "disposable" skill position player: draft a fast guy; plug him in; cut him when he loses a step, shreds a knee or breaks his brain.
If the NFL tries widening the field to save slot receivers, though, they could be in for a trial by fire.