by Scott Kacsmar

Arguably, the worst play a quarterback can make is throwing an interception. However, there are high amounts of luck and randomness involved with the rate at which interceptions occur. Sometimes the pass was tipped by the intended receiver. Sometimes the quarterback gets hit as he's throwing. Then you have the dozens of awful passes each season that should have been intercepted, but were dropped by defenders (reminding us why they play defense).

There's another type of play with negative consequences that is a much better predictor of future quarterback performance. The sack is a more common event that carries far less variation than the myriad of possibilities that come after a pass leaves the quarterback's hand. On these plays, the whole problem is the ball never did come out, and if it did, then we're looking at a fumble too.

Yet in all my years of following the NFL, it always seems like the sacks and fumbles are ignored in favor of the interception when it comes to analysis of a quarterback's mistakes. The sack is almost like a litmus test for where a fan is in their understanding of the game. Usually you start out thinking it's all about the offensive line and protection, but the sack is actually very dependent on the quarterback.

Peyton Manning led all quarterbacks in sack rate (2.66 percent) in 2013. Since entering the league in 1998, Manning has seven of the top 18 seasons in sack rate in that time. You can look at any other quarterback stat and Manning did not finish as high that frequently as he has with sack rate. Last year lowered his career rate to 3.10 percent, putting him above Dan Marino (3.13 percent) for the NFL record. As we looked at last year, Marino's quick release led to the greatest individual dominance of a stat in NFL history. He led the league in sack rate in seven consecutive seasons (1983-89) and 10 times overall.

Terrelle Pryor was just traded from Oakland to Seattle. Last season, he had a league-worst 10.23 percent sack rate. The Raiders were a mess at offensive line, but rookie Matt McGloin still managed a 2.77 percent sack rate (Manning territory) when he played. It's not like the Raiders magically blocked that much better for McGloin.

Since 2004, a quarterback has thrown at least 200 passes in back-to-back seasons 219 times. Here are the year-to-year correlation coefficients for six rate statistics in the passing game:

Year-to-year correlation (2004-13) Statistic Year-to-year correlation Completion percentage 0.54 Sack rate 0.52 Yards per attempt 0.47 Passer rating 0.42 Touchdown percentage 0.35 Interception percentage 0.05

See how untrustworthy interceptions can be? While a (usually young) player can certainly improve on limiting turnovers, it's the traits like accuracy and getting rid of the ball that are really more in his control.

To put it another way, sack avoidance is a great quarterback skill and most of the sacks that are taken are due to a failure in protection. But when the stat is presented for a quarterback's sack rate, it's an injustice to simply calculate sacks divided by the sum of passes and sacks. We looked at True Sack Rate last year and now return with the 2013 data that aims to quantify the rate at which quarterbacks are sacked.

2013's True Sack Rate

At its core, a sack is simply a pass play where the quarterback failed to get rid of the ball and gain positive yardage. A proper rate stat would include all of those plays, but the generic sack rate ignores scrambles on passes. From game charting, we add those scrambles along with counting intentional grounding penalties as sacks. After all, it's a quarterback under pressure, taking a loss of yardage. Those are even deadlier than the average sack due to the yardage involved. In January's wild AFC Wild Card game, the Chiefs' game-winning drive attempt was thwarted in large part to a 10-yard intentional grounding penalty charged to Alex Smith after pressure from Cory Redding. That set up a third-and-17 and knocked the Chiefs out of field-goal range. Smith actually would have saved at least three yards by taking the sack.

The following table sorts the leaders in True Sack Rate for all 37 qualified (minimum 224 pass attempts) passers in the 2013 regular season. General sack rate (Sack%) is also included with its ranking order. The number of accepted intentional grounding (IG) penalties is followed by the pass plays on which the quarterback scrambled (SCRAM). We also included just how many times the quarterback was under pressure (PRES) on those scrambles to differentiate from coverage scrambles or when a hole opened up. Stats are not adjusted for opponent.

Rk Quarterback Passes Sacks Sack% Rk IG SCRAM PRES Pct. TOT Passes True Sack Rate 1 Peyton Manning 659 18 2.66% 1 1 0 0 - 677 2.81% 2 Matthew Stafford 634 23 3.50% 2 3 11 6 54.5% 668 3.89% 3 Josh McCown 224 11 4.68% 3 0 8 7 87.5% 243 4.53% 4 Andy Dalton 586 29 4.72% 4 1 25 11 44.0% 640 4.69% 5 Jason Campbell 317 16 4.80% 5 1 12 7 58.3% 345 4.93% 6 Andrew Luck 570 32 5.32% 8 0 43 27 62.8% 645 4.96% 7 Philip Rivers 544 30 5.23% 7 0 15 7 46.7% 589 5.09% 8 Jay Cutler 355 19 5.08% 6 1 13 10 76.9% 387 5.17% 9 Ryan Fitzpatrick 350 21 5.66% 12 0 29 18 62.1% 400 5.25% 10 Sam Bradford 262 15 5.42% 10 0 7 4 57.1% 284 5.28% 11 Drew Brees 650 37 5.39% 9 1 12 7 58.3% 699 5.44% 12 Matt Cassel 254 16 5.93% 13 0 11 10 90.9% 281 5.69% 13 Matt Schaub 358 21 5.54% 11 1 4 1 25.0% 383 5.74% 14 Tom Brady 628 40 5.99% 14 1 3 1 33.3% 671 6.11% 15 Tony Romo 535 35 6.14% 15 1 8 3 37.5% 578 6.23% 16 Aaron Rodgers 290 21 6.75% 20 0 18 12 66.7% 329 6.38% 17 Matt Ryan 651 44 6.33% 16 2 8 6 75.0% 703 6.54% 18 Ben Roethlisberger 584 42 6.71% 19 0 14 8 57.1% 640 6.56% 19 Alex Smith 508 39 7.13% 23 1 46 23 50.0% 593 6.75% Rk Quarterback Passes Sacks Sack% Rk IG SCRAM PRES Pct. TOT Passes True Sack Rate 20 Carson Palmer 572 41 6.69% 18 2 5 4 80.0% 618 6.96% 21 Joe Flacco 614 48 7.25% 24 0 15 9 60.0% 677 7.09% 22 Case Keenum 253 19 6.99% 21 1 5 3 60.0% 277 7.22% 23 Chad Henne 503 38 7.02% 22 2 11 7 63.6% 552 7.25% 24 Eli Manning 551 39 6.61% 17 5 6 5 83.3% 596 7.38% 25 Robert Griffin 456 38 7.69% 25 2 37 27 73.0% 531 7.53% 26 Kellen Clemens 242 21 7.98% 26 0 9 8 88.9% 272 7.72% 27 Cam Newton 473 43 8.33% 28 0 38 26 68.4% 554 7.76% 28 Colin Kaepernick 416 39 8.57% 30 0 47 27 57.4% 502 7.77% 29 EJ Manuel 306 28 8.38% 29 1 26 14 53.8% 360 8.06% 30 Nick Foles 317 28 8.12% 27 2 18 6 33.3% 363 8.26% 31 Geno Smith 443 43 8.85% 32 0 31 17 54.8% 517 8.32% 32 Ryan Tannehill 588 58 8.98% 33 0 14 10 71.4% 660 8.79% 33 Mike Glennon 416 40 8.77% 31 2 12 7 58.3% 468 8.97% 34 Russell Wilson 407 44 9.76% 35 2 51 33 64.7% 502 9.16% 35 Christian Ponder 239 27 10.15% 36 0 25 10 40.0% 291 9.28% 36 Brandon Weeden 267 27 9.18% 34 1 7 2 28.6% 301 9.30% 37 Terrelle Pryor 272 31 10.23% 37 2 34 17 50.0% 337 9.79% AVERAGES 440.4 31.4 6.65% - 1.0 18.3 10.8 59.0% 490.1 6.60%

Rankings for the two sack rates barely change with the cumulative averages being 0.05 percentage points apart. That's to be expected given no quarterback can make his living off more than a couple of scrambles per game. What matters are the improved rates. Christian Ponder (+0.87%) had the biggest improvement. He was one of the more willing scramblers.

Eli Manning had the most negative change, dropping seven spots (-0.77%) in True Sack Rate thanks in part to his league-leading five intentional grounding penalties. He even had three in one game (Week 5 vs. Eagles). No quarterback since 2001 had more than two intentional grounding penalties in the same game. The average season only has about 35 grounding penalties, so they are not common at all. Eli's been charged with 11 since 2011 -- five more than runner-up Tom Brady. Eli's brother Peyton has eight intentional grounding penalties in his 240-game career.

Peyton Manning was also the only quarterback included here not to scramble once on 677 plays. For the second year in a row, Russell Wilson led all quarterbacks in scrambles to earn his "second coming of Fran Tarkenton" reputation. He had 50 as a rookie and 51 in 2013. He did face an above-average amount of pressure on the scrambles, but the highest rate belongs to Matt Cassel, who scrambled 11 times with 10 pressures. Nick Foles was one of the more notable names to have a low pressure rate, scrambling 18 times with six pressures (33.3 percent). He definitely showed more mobility in Chip Kelly's offense than expected and does not like to force passes.

2013 Sack Breakdown

Quarterbacks do react differently to pressure and some handle it better than others on a consistent basis. Now that we have a better sack rate, we can still break down the sacks even further through game charting to get a sense of the quarterback's sack avoidance skill.

Here's a brief guide to the sack categories in our charting:

Blown Block (BLOWN): Clear physical breakdown in protection that leads to the sack.

Coverage Sack (COV): A quarterback held the ball too long on a sack with sufficient protection.

Rusher Untouched (RUT): Often a blown assignment, these are the ugly plays where a rusher has a free run at the quarterback.

Other Pressure (OPRES): I lumped together plays that were charted as "Overall Pressure" (could mean multiple rushers) or "Blown Block/Rusher Untouched" (both could happen on same play).

QB Fault (QBF): Any time a quarterback "sacks himself" by tripping on his own feet, his lineman's feet, or just dropping the ball without being hit.

Failed Scramble (FS): On a pass play, the quarterback tried to scramble -- more because he saw room in front of him, as opposed to scrambling due to heavy pressure -- but the hole closed before he reached the line of scrimmage.

The following table shows how the 1,295 sacks in the 2013 regular season were marked in charting:

FO Charting Breakdown: 2013 Sacks Sack Type Total Pct. Total Sacks 1295 - Blown Block 743 57.37% Coverage Sack 264 20.39% Rusher Untouched 174 13.44% Other Pressure 75 5.79% QB Fault 13 1.00% Failed Scramble 26 2.01%

If we conclude that the coverage sacks and failed runs are mostly on the quarterback, then 76.6 percent of the sacks in 2013 were mostly due to protection failures. However, we know it's never as simple as the math suggests. Some quarterbacks do a much better job of helping the protection by getting rid of the ball quickly. An offense's usage of play-action and more deep routes will have a direct impact on the time the quarterback has to hold the ball, which will skew the sack numbers a bit.

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Still, we know some quarterbacks are taking bad sacks that would have been avoided by a different player. Case Keenum lost 23 yards on one sack in the fourth quarter against Arizona last year. Good luck getting Tom Brady down for that type of loss. He'd never retreat that far back.

Mobility is actually one of the most overrated attributes for a quarterback when it comes to avoiding sacks. The signal callers with excellent footwork in the pocket, capable of quickly identifying a target and releasing are the best at avoiding sacks. It doesn't matter that they couldn't break five seconds in a 40-yard dash. History has shown most of the highly sacked quarterbacks were mobile guys unwilling to give up on the play.

With that in mind, we'll conclude with a look at the 2013 breakdown by sack type for all 42 quarterbacks with at least 10 sacks taken.

Quarterback BLOWN Pct. COV Pct. RUT Pct. OPRES Pct. QBF Pct. FS Pct. Total Peyton Manning 17 94.4% (1) 0 0.0% (42) 0 0.0% (39) 0 0.0% (31) 1 5.6% (3) 0 0.0% (15) 18 Carson Palmer 33 80.5% (2) 2 4.9% (38) 2 4.9% (36) 3 7.3% (14) 1 2.4% (9) 0 0.0% (15) 41 Sam Bradford 12 80.0% (3) 1 6.7% (37) 1 6.7% (33) 0 0.0% (31) 0 0.0% (13) 1 6.7% (7) 15 Matt Schaub 16 76.2% (4) 1 4.8% (39) 1 4.8% (37) 3 14.3% (4) 0 0.0% (13) 0 0.0% (15) 21 Matt Ryan 33 75.0% (5) 5 11.4% (30) 4 9.1% (29) 1 2.3% (29) 1 2.3% (10) 0 0.0% (15) 44 Jake Locker 12 75.0% (5) 3 18.8% (26) 1 6.3% (35) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 16 Ryan Tannehill 43 74.1% (7) 6 10.3% (32) 6 10.3% (25) 2 3.4% (24) 0 0.0% (13) 1 1.7% (14) 58 Drew Brees 27 73.0% (8) 1 2.7% (41) 4 10.8% (24) 5 13.5% (5) 0 0.0% (13) 0 0.0% (15) 37 Andrew Luck 23 71.9% (9) 3 9.4% (35) 4 12.5% (21) 2 6.3% (16) 0 0.0% (13) 0 0.0% (15) 32 Christian Ponder 19 70.4% (10) 7 25.9% (16) 1 3.7% (38) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 27 Eli Manning 27 69.2% (11) 4 10.3% (33) 4 10.3% (26) 4 10.3% (9) 0 0.0% (13) 0 0.0% (15) 39 Tom Brady 27 67.5% (12) 6 15.0% (29) 5 12.5% (21) 2 5.0% (20) 0 0.0% (13) 0 0.0% (15) 40 Philip Rivers 20 66.7% (14) 8 26.7% (14) 0 0.0% (39) 1 3.3% (25) 0 0.0% (13) 1 3.3% (11) 30 Ben Roethlisberger 28 66.7% (13) 9 21.4% (21) 3 7.1% (31) 2 4.8% (21) 0 0.0% (13) 0 0.0% (15) 42 Chad Henne 25 65.8% (15) 3 7.9% (36) 7 18.4% (13) 2 5.3% (17) 1 2.6% (7) 0 0.0% (15) 38 Ryan Fitzpatrick 13 61.9% (16) 1 4.8% (39) 0 0.0% (39) 2 9.5% (11) 1 4.8% (4) 4 19.0% (1) 21 Alex Smith 24 61.5% (17) 9 23.1% (19) 4 10.3% (26) 2 5.1% (19) 0 0.0% (13) 0 0.0% (15) 39 Tony Romo 21 60.0% (18) 7 20.0% (24) 6 17.1% (17) 1 2.9% (26) 0 0.0% (13) 0 0.0% (15) 35 Jay Cutler 11 57.9% (19) 2 10.5% (31) 5 26.3% (3) 1 5.3% (18) 0 0.0% (13) 0 0.0% (15) 19 Kellen Clemens 12 57.1% (20) 2 9.5% (34) 7 33.3% (2) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 21 Jason Campbell 9 56.3% (21) 5 31.3% (7) 2 12.5% (21) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 16 Quarterback BLOWN Pct. COV Pct. RUT Pct. OPRES Pct. QBF Pct. FS Pct. Total Andy Dalton 16 55.2% (22) 5 17.2% (27) 5 17.2% (16) 3 10.3% (8) 0 0.0% (13) 0 0.0% (15) 29 Aaron Rodgers 11 52.4% (23) 6 28.6% (11) 2 9.5% (28) 0 0.0% (31) 0 0.0% (13) 2 9.5% (5) 21 Joe Flacco 25 52.1% (24) 11 22.9% (20) 9 18.8% (11) 2 4.2% (22) 1 2.1% (12) 0 0.0% (15) 48 Brandon Weeden 14 51.9% (25) 8 29.6% (9) 2 7.4% (30) 2 7.4% (13) 0 0.0% (13) 1 3.7% (9) 27 Cam Newton 22 51.2% (26) 15 34.9% (3) 3 7.0% (32) 3 7.0% (15) 0 0.0% (13) 0 0.0% (15) 43 Colin Kaepernick 19 48.7% (27) 11 28.2% (12) 5 12.8% (20) 1 2.6% (28) 0 0.0% (13) 3 7.7% (6) 39 Matthew Stafford 11 47.8% (28) 6 26.1% (15) 5 21.7% (8) 0 0.0% (31) 1 4.3% (5) 0 0.0% (15) 23 Michael Vick 7 46.7% (29) 3 20.0% (24) 1 6.7% (33) 3 20.0% (3) 1 6.7% (2) 0 0.0% (15) 15 Matt Flynn 11 45.8% (30) 5 20.8% (23) 5 20.8% (10) 3 12.5% (6) 0 0.0% (13) 0 0.0% (15) 24 Josh McCown 5 45.5% (31) 3 27.3% (13) 0 0.0% (39) 0 0.0% (31) 1 9.1% (1) 2 18.2% (2) 11 Russell Wilson 20 45.5% (31) 14 31.8% (6) 8 18.2% (14) 1 2.3% (29) 1 2.3% (10) 0 0.0% (15) 44 Nick Foles 12 42.9% (33) 10 35.7% (2) 4 14.3% (19) 1 3.6% (23) 0 0.0% (13) 1 3.6% (10) 28 Robert Griffin 16 42.1% (34) 11 28.9% (10) 9 23.7% (5) 1 2.6% (27) 0 0.0% (13) 1 2.6% (12) 38 Mike Glennon 16 40.0% (35) 13 32.5% (5) 7 17.5% (15) 3 7.5% (12) 1 2.5% (8) 0 0.0% (15) 40 EJ Manuel 11 39.3% (36) 11 39.3% (1) 6 21.4% (9) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 28 Thad Lewis 7 38.9% (37) 6 33.3% (4) 4 22.2% (7) 0 0.0% (31) 0 0.0% (13) 1 5.6% (8) 18 Case Keenum 7 36.8% (38) 4 21.1% (22) 8 42.1% (1) 0 0.0% (31) 0 0.0% (13) 0 0.0% (15) 19 Geno Smith 15 34.9% (39) 10 23.3% (18) 8 18.6% (12) 9 20.9% (2) 0 0.0% (13) 1 2.3% (13) 43 Blaine Gabbert 4 33.3% (40) 2 16.7% (28) 2 16.7% (18) 4 33.3% (1) 0 0.0% (13) 0 0.0% (15) 12 Terrelle Pryor 9 29.0% (41) 8 25.8% (17) 7 22.6% (6) 3 9.7% (10) 1 3.2% (6) 3 9.7% (4) 31 Matt Cassel 3 18.8% (42) 5 31.3% (7) 4 25.0% (4) 2 12.5% (6) 0 0.0% (13) 2 12.5% (3) 16

All but one of the 18 sacks taken by Peyton Manning were blown blocks. That's the highest rate in the league and he's the only quarterback here to not take a coverage sack. Many of the quarterbacks with a low rate of blown block sacks and high rate of coverage sacks are inexperienced (Terrelle Pryor, EJ Manuel, Mike Glennon and Thad Lewis) or just not very good (Cassel).

Cam Newton led the league with 15 coverage sacks. If he was waiting for guys like Steve Smith and Brandon LaFell to get open, then that might be a problem in 2014 with Jerricho Cotchery and Jason Avant currently leading the receiving corps.

Joe Flacco and Robert Griffin III had the most sacks with a rusher untouched (nine), but Keenum had the highest rate of his sacks happening that way. Houston signed Ryan Fitzpatrick this offseason, but he led the league with four failed scrambles resulting in sacks.

Yeah, the Texans could use a quarterback, but if the history of sack rates is any indication, Johnny Manziel's maverick style may keep him in David Carr territory (read: the bottom) on any future list of True Sack Rates.