Pro Football Reference Blog

It's always difficult to compare players across eras, and at no place is the discrepancy more complicated than at quarterback. Many traditional quarterback statistics such as completion percentage, passing yards and touchdown-to-interception ratio, have risen significantly over the past few decades. On the other hand, quarterbacks are starting at younger ages now than ever before, a combination of rising salaries for rookies and the NFL's decision to allow players just three years removed from high school to enter the draft. Matthew Stafford and Josh Freeman are two of the youngest four players to throw for 300 yards in a game. And while Mark Sanchez and Sam Bradford aren't super young, they were thrown into the fire immediately. Both were opening day starters for their teams despite limited college experience: Sam Bradford threw at least 10 passes in only 29 games in college; Sanchez hit that number in just 16 games.

In some ways, the effects can cancel out. Maybe a 24-year-old quarterback who sat on the bench for 2 seasons but played in the '70s is similar to a 21-year-old rookie starter in 2009. But it's important to compare apples to apples, or at least to recognize which fruits you're comparing. For that reason, I'm going to take a look at how Bradford, Sanchez and Freeman are doing -- era-adjusted, of course -- in three different ways: how they played by experience, by age, and by seasons starting.

First, against which quarterbacks should we compare these three (and Matthew Stafford)? I took 30 or so of the best and most famous since the merger. Why the best? If these guys can hold their own against the all-time greats, then for all their criticism, their potential should still look strong. Here's the full list of quarterbacks:

Let's look at how all of the above quarterbacks performed as rookies, with only players with at least 225 pass attempts being considered. I compared how the quarterback performed relative to league average in several key statistics. A 117 in y/a means the QB averaged 17% more yards per pass than league average that season. All numbers over 100 are good, including interception percentage.

My preferred stat to judge rookie quarterbacks is net yards per attempt. ANY/A is explanatory of past results, but is too sensitive to interceptions to be a strong predictor of future performance. Net yards per attempt is a great way of seeing how well a quarterback is playing on a conssitent basis. What's interesting about Bradford? He ranks last among the quarterbacks listed in NY/A, averaging only 82% as many net yards per pass as the average quarterback this season. To be fair, he's not far behind a couple of Hall of Famers in Aikman and Elway. He looks much better in terms of completion percentage, but what does that mean? Bradford is dinking and dunking, belying his reputation as a gunslinger. The Rams' offensive line isn't very good and they lack a deep threat, so it makes sense for him to emphasize the short passing game. Still, it's a little surprising to see that Bradford ranks dead last in yards per completion among the 33 QBs in the NFL this season.

As far as winning goes, it's going to be impossible to top Roethlisberger's 13-0 mark. Marino (7-2) and Ryan (11-5) also stand out as excellent, with Sanchez' 9-7 mark last season the only other quarterback on the list with a winning record and at least eight starts. Also worth remembering that Peyton Manning and Troy Aikman were a combined 3-24 as rookies. By that measure, Bradford -- also inheriting a terrible team by virtue of being the first overall selection -- looks downright impressive at 4-6. Then again, he does play in the NFC West, maybe the worst division ever; and that was before last week's showing, when the teams went 0-4 and were outscored by 71 points on Sunday.

Stafford and Freeman look relatively good on this list, and that's before considering their age. In fact, they were the only rookies on the list to even enter the league at age 21. Bradford is 23 years old -- how does he compare at that age to other quarterbacks?

Once again, pretty low on the list, but a lot of these players also sat on the bench at this age. He's got the impressive INT rate, but that may also be correlated with his low-risk style of offense. The Rams are lacking talent across the board, but so were some of the other teams the above quarterbacks played on. Bradford certainly looks like he has "it", but at this he has been less impressive as far as NY/A than the other quarterbacks at that age.

This may disadvantage Bradford to compare him to nonrookies, but how does he compare as a first-year starter to the others in their first years starting?

As expected, Bradford looks pretty bad here, even among those his age. Of course, he's sandwiched between Aikman and Young, so it's not all bad. And many of these players were on betters teams, especially among those who started at a later age. But if you really wanted to throw cold water on the Sam Bradford express, the table above would be how to do it.

What about second year quarterbacks Sanchez and Freeman? How do QBs who are playing in their second season (according to draft year, not playing status) look?

A bunch of quarterbacks took the league by storm in their second season, but a good chunk of them were still around league average or not even playing two years out from their draft. Bert Jones, Steve Young, Dan Fouts, Warren Moon and -- gasp -- Joe Montana all had ugly winning percentages in their second years in the league. For Sanchez, the most concerning number on there is his ugly completion percentage, worse than every quarterback on the list save Vinny Testaverde.

Freeman and Sanchez are having similar years -- they're around league average in NY/A, but have used great INT rates and some good fortune to post strong records. But one reason to be much higher on Freeman's potential -- his age. Sanchez is only 14 months older than Freeman, but because of his January birthday, Freeman gets technically recorded as a 22-year-old QB for this season. And that puts him in rare company:

Of all the great quarterbacks on this list, only five of threw 225 passes at 22 years of age. Freeman compares favorably to Kosar and Manning at that age, and isn't far behind Roethlisberger and Marino. This analysis probably overrates Freeman slightly because he's an "old" 22, but he still looks to have as much potential as any quarterback drafted in the past few seasons. Sanchez? He's a "young" 24 this season -- his birthday was a couple of weeks ago -- but how does he compare?

He looks great as far as winning percentage and interception rate, but those aren't highly correlated with quarterback ability. Still, he looks more than respectable in NY/A, ANY/A and Y/A. On the other hand, his completion percentage at age 24 is even worse relative to league average than Bradshaw's was. Because he's been far below average in that category two years in a row, it's a legitimate concern. It also makes it even harder to put much faith in his low interception rate this year. Still, NY/A matters more than completion percentage, and Sanchez is tied with Montana and Brady in that category. Not bad company.

What about comparing Sanchez and Freeman to other second year starters, regardless of age or experience level? Obviously this will put both of them behind the 8-ball, especially Freeman:

Players like Stabler, Young and Warner have a big advantage here, not starting their second season until they were 29 or 30. Still, Sanchez and Freeman look pretty impressive. They were better than Kelly or Brady or McNabb or Moon, all of whom were older. They're below average on this list, but it's the one inherently biased against them and a list of the best quarterbacks in the past 30 years. At this point, by any measure, the futures for Sanchez and Freeman look bright.