How many times have you heard about a "bend-but-don't-break" defense – you know, a defense that seems to give up a lot of yards, but stiffens with its back up against the goal line?

We're willing to bet not a single pregame show or football broadcast goes by without someone throwing out the phrase. Of course, many broadcasters, prognosticators and "pundits" are more interested in filling airtime than they are in leading you down the path of pigskin enlightenment.

Enter the Pythagoras of gridiron arithmetic, the Cold, Hard Football Facts.

We decided to quantify for the first time in the history of footballkind the "bend but don't break" phenomenon. It allowed us to determine the most bendable defenses in the NFL and, of course, the most easily broken. It was quite easy to do.

The NFL rates total defense by the number of yards surrendered. It considers points allowed a separate defensive category. But somewhere between these numbers lie the most bendable and most brittle defenses in football.

We simply divided each team's yards allowed by points allowed. What it gave us was "yards per point allowed" – the number of yards an opposing team must generate to score a single point. The greater the number, the more flexible the defense. The smaller the number, the more brittle the defense. You can get a feel for which defenses are the most bendable simply by looking at the spread between their total-defense ranking and points-allowed ranking.

Philadelphia, for example, ranks just 24th in total defense (348.5 yards per game) but is second in points allowed (16.4). It turns out the Stretch Armstrong Eagles top our list of the most bendable defenses in football. Opposing offenses must generate more than 21 yards for every point they score against the Eagles.

San Francisco, meanwhile, inhabits the other end of the flexibility spectrum. The 49ers rate a respectable 15th in total defense (333.0 yards per game, well ahead of Philly) but a woeful 31st in points allowed (28.0). The 49ers, we discovered, have the most peanut butter-brittle defense in the NFL, giving up a point for every 11.89 yards allowed – nearly half the number of yards teams must generate to score against Philadelphia. We were actually startled by the vast difference between the best and worst defenses on our flexibility list.

Yards per point allowed is a simple calculation but it ultimately accounts for a number of variables -- field position, special teams proficiency, red zone defense and turnovers -- in a succint little package that show us which defenses may bend, but refuse to break.

Here's the ranking of the most bendable defenses in the NFL, from the Gumby-like spine of the Philadelphia Eagles to the osteoporosis-riddled bones of the San Francisco 49ers.

1) Philadelphia – 21.28 yards per point allowed
2) Baltimore – 19.89
3) Jacksonville – 18.73
4) New England – 18.58
5) New York Jets – 18.38
6) New York Giants – 17.87
7) Chicago – 17.67
8) Seattle – 17.27
9) Atlanta – 17.00
10) San Diego – 16.69
11) Cincinnati – 16.64
12) Arizona – 16.40
13) Detroit – 16.10
14) Houston – 16.07
15) Denver – 16.02
16) Washington – 15.70
17) Buffalo – 15.66
18) Indianapolis – 15.64
19) Cleveland – 15.33
20) Pittsburgh – 15.28
21) Tampa Bay – 14.98
22) Tennessee – 14.89
23) Minnesota – 14.79
24) Green Bay – 14.40
25) Miami – 14.31
26) New Orleans – 14.18
27) Carolina – 14.17
28) St. Louis – 13.80
29) Dallas – 13.43
30) Kansas City – 13.25
31) Oakland – 12.59
32) San Francisco – 11.89

It turns out bendability is a key to team success. Twelve of the teams in the top half of our list are .500 or better. The bottom half is inhabited by just three teams with winning records.