The play below was special for a lot of reasons. It decided that year’s Iron Bowl blood feud and SEC West race. But its memorability is also due in large part to how it happened. The kick six — the unblocked field goal returned for a touchdown — is one of football’s rarest and most shocking plays.

The ending to 2013 Alabama-Auburn is now a proper noun, the Kick Six. It’s the kind of play that seers itself into a fan’s mind. A lot of us remember where we were when Chris Davis caught a 56-yarder that came up short and ran it back 109.

Sometimes, field goal attempts turn into TDs. But a true kick six, when the ball isn’t blocked but gets returned for a score anyway, is its own rarity.

By far the most common way for a field goal attempt to become a touchdown is for the kick to get blocked and the defense to scoop up the ball. There have been 37 of these plays in the NFL alone since 1994, according to the play index at Pro Football Reference.

Those are block sixes. A true kick six is a different level of unlikely.

The NFL has had five kick sixes since ‘94, compared to those 37 block sixes.

Here’s more math, via PFR:

Since 1994, there have been 23,846 NFL field goal attempts, counting playoffs.

2,529 have come from 50 yards or deeper.

Five attempts, in total, have become kick sixes.

Kick sixes are harder to track in college, but they’re really rare there, too.

Earlier in the 2013 season, Odell Beckham Jr. had one for LSU:

Since Auburn’s big moment, there’s only been one in a huge college game, scored by Houston against Oklahoma in Week 1 of 2016.

College football doesn’t have detailed play-by-play databases to tell us how often kick sixes happen. Broadly, the answer is “almost never.”

And, of course, there’s no telling how often they happen at the even less database-friendly high school level. But it does happen, as it did in Michigan in 2013, a few weeks before it happened at Auburn ...

... and in Tennessee in 2016:

Baseball teams even do it sometimes:

Like a reenactment of a war battle.

Why are these plays so rare? So many things have to fall into place. Auburn’s return against Alabama is a good illustration.

The kicking team has to be attempting a long field goal, and it has to miss short. The returning team has to give up a potential kick-blocker to send someone back to field an attempt that comes up short. And if the kick does fall short, the returner has to catch it and elude trouble for approximately 100 yards.

Teams are more likely to try long field goals when the kick is guaranteed to be the last play of a half. The opposition is more likely to send someone back to field a short kick in those moments, when there’s no field-position risk to worry about on a runback.

Houston’s kick six came in the middle of the third quarter, and the Cougars put Brandon Wilson back deep because Oklahoma was trying a 53-yarder with a college kicker. If the Sooners weren’t losing by two in the second half, they might not have tried the kick at all.

What made the Kick Six even more special: these plays usually aren’t all that important.

The NFL’s five recent examples:

1998: The Jets’ Aaron Glenn: 104 yards off the Colts’ Mike Vanderjagt. Glenn’s Jets gave up 14 unanswered points after his kick six took them into halftime with a 13-point lead.

2002: The Ravens’ Chris McAlister: 107 yards off the Broncos’ Jason Elam, making a 24-3 Ravens lead into a 31-3 lead.

2005: The Bears’ Nathan Vasher: 108 yards off the Giants’ Joe Nedney:

Vasher’s return provided the go-ahead points in a win, though it happened in the second quarter.

2006: The Bears’ Devin Hester: 108 yards off the Giants’ Jay Feely, though Chicago wouldn’t need the points.

2007: The Chargers’ Antonio Cromartie: 109 yards off the Vikings’ Ryan Longwell. The Chargers then lost.

None of those five was anywhere near as dramatic as the Auburn return.

The Bears getting two of these things in two years (Vasher and Hester in ‘05 and ‘06) is one of the wildest statistical anomalies ever. That should never happen again.

What’s your favorite kick six? Did I miss one somewhere?

Probably. This sport’s weird.