When former Chicago Bears receiver Johnny Knox felt the career-altering hit on Dec. 13, 2011, he knew something was definitely wrong. 

After fumbling near the end of the 17-yard catch against the Seattle Seahawks, Knox instinctively scrambled towards the exposed football. Almost simultaneously, 285-pound defensive tackle Anthony Hargrove hit Knox from the front—forcing his body to bend backwards in what now serves as an ugly and tragic end to a promising football career.

“When they turned me over, that was the worst pain I’ve ever felt," Knox told Sean Jensen of the Chicago Sun Times. 

Somehow, his legs and arms were fully functional. No paralysis. That was the good news. But Knox needed a stretcher to get off the field, and an ambulance rushed the 24-year-old receiver to a local hospital. 

Once there, Knox would need a stabilizing surgery for his mangled, fractured vertebrae. The official diagnosis? A thoracic-lumbar junction fracture-dislocation, with significant nerve damage. The middle of his back was cracked.

Fourteen months following his spinal fusion, Knox's football career is now all but over. 

The Bears officially terminated Knox's contract Tuesday, and he confirmed to Jensen that it's time to move past playing football again. 

As an athlete, you don’t want to give up, you want to keep on fighting. That’s how I’ve always been. But it’s been on my heart for a while. I know how my body feels, and I know I’m not going to be the same and perform at the ability that I used to.

So I’m moving on and going forward.

And just like that, the football story of Johnny Knox had written its last chapter. Such a tragic conclusion doesn't seem to do the original narrative justice. Underdog stories aren't supposed to end like this. 

A first-team all-state selection from Channelview, Texas, Knox received very little college attention following high school. And that didn't just include from Division I colleges. The disregard of Knox and his football dreams included just about everyone. 

A junior college head coach in Kansas wouldn't even talk to Knox about a potential scholarship, according to Lindsey Willhite of the Chicago Daily (via Tyler Junior College athletics). At a camp that showcased potential junior college players, Knox received a grade of "3," while other top JUCOs received "1s."

This painful pursuit has killed the dreams of many high school football players. At some point, most realize that playing the game isn't in their future. Undeterred, Knox continued his exhaustive search.

Finally, he found a home at Tyler Community College, who somewhat reluctantly had an open spot at wide receiver. Once on life support, Knox's football career would go on at the junior college. 

During his sophomore season at Tyler, Knox finally started to put everything together. With his speed emerging as an invaluable asset, Knox caught 11 touchdowns and averaged almost 24 yards a catch—both of which led all Texas junior colleges.

But once again, when his two years in Tyler ended, none of the big schools came calling. There was no offer from Texas. Or Texas A&M. Or Texas Tech. Under the radar Knox remained. 

In 2007, Knox transferred to Abilene Christian, a small, Division II school in northern Texas with less than 5,000 total enrolled students. Abilene wasn't under the bright lights of Austin or College Station or Lubbock. But Knox's football career would go on. 

Maybe the NFL was still a dream for Knox at this point, maybe it wasn't. Among ACU alums was NFL safety Danieal Manning, but very few make the galactic jump from JUCO to Division II to the NFL. 

Knox set out to do just that. 

In his first season at ACU, Knox caught 62 passes for 1,158 yards and a school- and conference-record 17 touchdowns over 13 starts. For his efforts, he was named a second-team All-American and first-team All-Southwest region. 

The next season, Knox started to put his name into the NFL consciousness with 56 catches for 1,069 yards and 13 touchdowns. In two seasons at ACU, the speedster went over 2,200 yards and caught 30 scores, while also returning punts and kicks.

Despite the statistical production, it still took a standout performance from Knox at the Texas vs. the Nation All-Star game to lock in an invite to the NFL scouting combine. Knox then stole the show in Indianapolis, finally establishing himself as a selectable player in the 2009 NFL draft.

Standing 6'0" and weighing just 190 pounds, Knox ran the 40-yard dash in a blazing 4.34 seconds. His time clocked in just behind Maryland's Darius Heyward-Bey (4.30 seconds) and Mississippi's Mike Wallace (4.33) for the fastest man at the 2009 combine. 

The NFL had suddenly been put on notice. 

Pure speed is something you can't teach, and Knox had fast spilling out his pores. While unrefined as a receiver, Knox possessed the kind of straight-line explosion that the NFL constantly drools over. 

That following April, dream become reality for Knox. 

The Chicago Bears, while debating what they wanted to do with the fourth pick in the fifth round, came across Knox's name. Then general manager Jerry Angelo described the process of picking Knox to the Bears official site:

We were in the fifth round of the draft and Lovie [Smith] looked at the board along with the scouts and said, “How about this Johnny Knox?” He said, “We really don’t have anybody like him.” We all talked together and we thought given the other players that we were considering that he had the traits we look for at the position. He was probably a little bit more unknown given his level of competition [at Division II Abilene Christian], but we knew that with Jay [Cutler] being on board, [Knox] could be another potential weapon, so we went ahead with it.

Angelo admitted the pick was a risk, even in the fifth round, and that Knox had nothing more than a "50/50" chance of making the team the next September. 

Right away, Knox looked like he belonged.

In the preseason, he caught five passes for 127 yards—including 43-yarders in back-to-back games to close the exhibition schedule. The explosion he put on display at the combine was translating to the next level. Knox made the team. His football career would go on. 

During the 2009 season, Knox would catch 45 passes for 527 yards and five touchdowns. Seven of his catches went for 20 or more yards. He also racked up 927 yards returning kicks, including a 102-yard touchdown. Knox was named to the Pro Bowl as a special teamer after Percy Harvin was forced out to injury. 

The next season, he would lead the Bears in receiving yards with 960 and touchdown receptions with five. His 17 catches of 20 or more yards was good enough for 10th in the NFL. 

While 2011 wasn't as kind to Knox—he was on pace for less catches, yards, touchdowns and 20-yard plays than in 2010—he still averaged nearly 19 yards a catch as Jay Cutler's main receiving target. 

Knox likely wasn't a prototypical No. 1 receiver, and few argued against the Bears needing to add help at receiver. But for three productive seasons, the former high school star who couldn't find a JUCO coach to take him in was starring in a featured role for an NFL offense. For the time being, it appeared Knox's football career would continue going on. 

Then, disaster struck. Just one unlucky bounce, one unfortunate hit, and it all ended for Johnny Knox. That December afternoon changed the entire narrative. 

To start last season—the first following his spinal fusion—the Bears predictably placed Knox on the Physically Unable to Perform (PUP) list. When he was unable to return later in the season, he landed on injured reserve—and questions about whether or not he'd ever play in the NFL again become a real possibility. 

Now, 14 months after the hit, Knox is giving in to the reality that the injury has eliminated his ability to play the game. He's not bitter, or resentful, but more appreciative to simply be able to walk. 

"I was centimeters away from being paralyzed, so just sitting here and talking, I’m appreciative of that,” Knox told Jensen. 

No, Knox's underdog story doesn't have a Hollywood ending. His rags-to-riches journey won't end with him strutting onto Solider Field in 2013 or catching the game-winning catch in the Super Bowl. 

It's certainly not the conclusion anyone wanted. For the first time in his life, Knox's football career won't go on.