Chase Stuart writes about the historical and statistical side of football at his site, FootballPerspective.com

After seven weeks, Robert Griffin III of the Redskins has exceeded even the most optimistic expectations. He leads the N.F.L. with a 70.4 completion percentage, and could become the first rookie to lead the league in that category since Parker Hall with the Rams in 1939.

Griffin also ranks first in yards per attempt with an 8.5 average, and could become the first rookie since another Ram, Bob Waterfield in 1945, to lead the N.F.L. in that statistic. Only two rookies in professional football history have ever led the league in both completion percentage and yards per attempt. The first was another Redskin, Sammy Baugh, in 1937; the last was Greg Cook, in the American Football League in 1969 (his career was ruined by a shoulder injury that year).

Griffin’s statistical domination of the record book has been astounding. And that’s before we get to the fact that he has 468 rushing yards and 6 touchdowns in seven games, putting Cam Newton’s rookie rushing records in both categories (706 and 14) in jeopardy.

Griffin will always be compared to the man selected one spot before him in the 2012 draft, Andrew Luck. And on the surface, there’s no comparison. Luck ranks 32nd in completion percentage (53.6) and 25th in yards per attempt (6.7). Whereas Griffin ranks third in traditional passer rating (101.8) behind Aaron Rodgers and Peyton Manning, Luck is tied with Brandon Weeden (72.3) and ahead of only Matt Cassel for last place.

But traditional statistics don’t always tell the full story, especially when we’re dealing with a sample size that’s smaller than half a season. Those watching Luck have usually come away thinking that he’s the next great quarterback, despite the raw numbers. Fortunately, there’s a way to fill in the rather large gap between perception and statistical production. One of those tools is ESPN’s Total QBR, which ranks Luck as the sixth-best quarterback in the N.F.L. this season. That’s even ahead of Griffin, who is eighth in QBR.

Jeff Bennett of ESPN Stats & Information, in a telephone interview, was able to help explain why Luck was not only the best rookie quarterback this season, but also perhaps the most underrated quarterback in the N.F.L.

Difficulty of Throws

It’s a gross generalization, but Luck plays in a vertical offense while Griffin plays in a horizontal one. Griffin ranks first in completion percentage while Luck ranks 32nd, but that has as much to do with the throws they’re asked to make as each quarterback’s accuracy. Luck‘s average pass attempt has traveled 10.2 yards past the line of scrimmage, the longest average pass distance in the league (this was before “Monday Night Football”; Jay Cutler was second at 9.9 entering the game). Griffin averages 7.9 yards downfield per pass attempt, slightly below the league average of 8.2.

And Luck’s long average pass distance isn’t simply a product of throwing lots of incomplete passes down the field. His average pass distance on completions is 8.6 yards past the line of scrimmage, also highest in the N.F.L. (Cutler was fourth at 8.3 entering Monday night). Griffin’s completions come an average of 5.8 yards from the line of scrimmage, well below the league average of 6.5.

Those numbers agree with Brian Burke’s data at Advanced NFL Stats, which show that Griffin has thrown only 14 percent of his passes 15-plus yards past the line of scrimmage, the lowest rate in the league. Luck has thrown only 11 percent of his passes at or behind the line of scrimmage, while Griffin is in an offense that has let him throw 44 passes at or behind the line, accounting for 23 percent of his attempts. Coach Mike Shanahan and his offensive coordinator, Kyle Shanahan, deserve credit for molding an offense that fits Griffin’s strengths. Unfortunately for Luck, nothing is being made easy for him in Indianapolis.

Yards After the Catch

Casting Luck as a downfield thrower is true, but only half the story. Unlike many rookie quarterbacks, whether through design or lack of talent, Luck rarely has a running back as a checkdown option. According to Footballguys.com, Colts running backs have been targeted on just 7 percent of all Indianapolis passes, the lowest mark in the league. Conversely, Colts receivers have been targeted on 72 percent of Indianapolis attempts, the highest mark in the N.F.L.

In the same vein, much of Griffin’s production has come via yards after the catch. On average, passers in 2012 have gained 56 percent of their yards through the air and 44 percent on yards after the catch by their receivers. For Griffin, 51.4 percent of his yards have come via his receivers after the catch, the fifth-highest mark in the league. Luck, in large part because of his downfield passing, has gained 68.9 percent of his yards through the air, the highest percentage in the league, and therefore has been helped the least in terms of yards after the catch.

However, simply putting the stats in this context does not mean that Luck has been a better passer than Griffin; rather, it is to simply close the extraordinary gap created by traditional statistics. Griffin’s completion percentage and yards per attempt average are still more impressive even after adjusting for the difficulty of his throws. If we looked simply at their passing numbers, even ESPN’s Total QBR would rank Griffin ahead of Luck, by a score of 68.7 to 60.7. And while you know there is more to being a quarterback than just passing, you might be surprised to learn that looking at those things actually vaults Luck ahead of Griffin.

Running for Purpose

Griffin has rushed for 468 yards, averaged 7.6 yards per carry and scored six touchdowns, while Luck has rushed for only 115 yards on 5.8 yards per carry and scored three touchdowns. But according to ESPN, Luck has been the more valuable runner this year. How can that be?

Luck has only 18 true carries this season, with 2 of his 20 carries coming on kneel-downs. Luck doesn’t run very often, choosing his spots carefully. Despite only 18 true rushes, Luck has 10 first-down runs on scrambles, most in the league (Griffin and Michael Vick each have nine). Seven of those 10 have come on third down; no other quarterback more than 4 scrambles for 1st downs on 3rd down this year. Over all, 12 of his 18 runs have gone for first downs, while Griffin has gained first downs on only 41 percent of his 61 runs (excluding kneel-downs).

Another reason Griffin’s rushing value is depressed in ESPN’s system is that he has five fumbles on rushing plays this season and has only recovered one (his teammates have recovered two). Luck has yet to fumble on a running play this year. Add it all up, and Luck has a near-perfect rating of 99.8 on runs this season, while Griffin has an impressive but less stellar 78.8 rating.

Once you take rushing and passing – and the context in which they occurred – into account, Luck and Griffin are actually closer than the traditional statistics may indicate. And context is particularly important to Luck.

Clutch Performances

One other factor that bridges the gap between the traditional stats of the two quarterbacks is clutch performance. ESPN adds an element to its calculation that gives quarterbacks more credit (or blame) for their performance in high-leverage plays. This is designed to quantify a player’s performance in the clutch. As a general rule, statisticians agree that clutch performance is not predictable or repeatable, but no one doubts its impact in explaining what happened. So while Luck may not continue to be a particularly clutch quarterback, he certainly has played well in crucial situations so far in his early career.

To judge the impact of this clutch weighting properly, ESPN internally ran QBR calculation without that weighting – that is, counting all contributions the same regardless of the time/score situation. According to Bennett, in that light, Griffin edges Luck by a 10-point margin in Total QBR, 75.7 to 65.8. But once you account for the potential impact of each play by taking into account the game situation (which is already incorporated into the passing/running QBR numbers mentioned above), Griffin slides down a bit and Luck moves up, giving Luck the small margin over his rookie counterpart in Total QBR, 73.0 to 71.8.

Luck led a memorable fourth-quarter comeback against the Green Bay Packers, and he also led a game-winning drive against the Vikings in the final 31 seconds. He nearly had a third memorable performance: against the Jaguars, He led a fourth-quarter comeback, giving the Colts a the lead with one minute to go. After a quick Jacksonville touchdown, he nearly led Indianapolis back to victory.

Hidden Factors

Another metric that traditional individual stats ignore is penalties. Luck has added more value to his team on called penalties, like defensive pass interference and defensive holding, than any other quarterback in the league. Griffin has also been drawing key flags — he ranks third in value added via penalty — a sign that both quarterbacks are putting stress on defenses.

Technically, ESPN does not take into account the strength of opposing defenses, but Bennett and his team have come up with a “defense-adjusted” QBR. Luck has faced tougher defenses this season (Chicago in particular, along with Green Bay and the Jets), and his opponent-adjusted Total QBR is 75.4. While Griffin’s schedule hasn’t been full of cupcakes, it has been below average, and the opponent-adjustment brings him down to 67.2.

Conclusion

Both Andrew Luck and Robert Griffin III have been excellent this year, but only Griffin looks great when examining traditional metrics. The above analysis isn’t intended to denigrate Griffin; if anything, it should raise questions about why the coaches in Indianapolis are making things so difficult for Luck. He has being asked to throw more deep passes and has made fewer checkdowns than just about any quarterback in the league, despite an extremely inexperienced set of targets after Reggie Wayne. He has also being asked to throw the ball frequently — he ranks third in pass attempts per game, the cost of doing business when paired with a below-average defense and an anemic running game. As a result, his completion percentage and yards per attempt averages are underwhelming, but it’s tough to say how well Griffin would do if the players switched teams. Griffin may have the highlight reel runs and the showy statistics, but Luck has arguably been even more impressive under considerably more challenging circumstances.