From the Washington Post:

The wide-open era
Led by some of the NFL's current greats, quarterback play is as exciting and efficient as ever

"There are a lot of quarterbacks playing at a high level, more than I've seen in a long time," former Washington Redskins quarterback Joe Theismann said.

If this indeed becomes one of the greatest seasons for quarterbacks, collectively, in league history, the question will be: Why now?

The answer seems to be that it's a combination of having a collection of excellent quarterbacks and a set of circumstances highly favorable to good quarterback play. ...

But it's more than just an assemblage of good quarterbacks. It's also the most passing-friendly era in NFL history. The game has been wide open since the 2004 season, before which the league cracked down on clutching-and-grabbing tactics by defensive backs with a directive from the competition committee to officials to strictly enforce the rule prohibiting defensive contact against receivers more than five yards downfield.

Actually, after the pass-happy 2004, referees tended to shift against the offense again, as Aaron Schatz of FootballOutsiders pointed out in 2005. Maybe the way the refs are calling has shifted back in 2009 to more 2004-like customs? The NFL can change things by winks and nudges as well as by overt rule changes.

The game changed immediately. That season, Peyton Manning threw 49 touchdown passes, breaking Dan Marino's 20-year-old NFL season record, and had the highest passer rating in league history, at 121.1. Brady threw 50 touchdown passes two seasons ago to set a new record. Last season, Brees had only the second 5,000-yard passing season in NFL history. Add to that the fact that the league has cracked down on hits on quarterbacks by defenders, and stopping the top passers seems to have become next to impossible.

"I think the rules benefit the passing game right now," said Tim Hasselbeck, a former quarterback for five NFL teams, including the Redskins and New York Giants. "You have the way pass interference and the plays down the field are being called. You have quarterbacks being protected by the rules, and I think that obviously plays into it. It helps guys stay healthy and play every week."

Peyton Manning and Roethlisberger are on pace for 5,000-yard passing seasons. Perhaps more strikingly, eight NFL quarterbacks currently have passer ratings above 100. Six more have passer ratings above 90. Compare that to last season, when only the San Diego Chargers' Rivers had a passer rating above 100 at season's end, and eight others topped 90.

The passer rating is a figure designed to assess overall throwing efficiency through a complicated formula that takes many statistical elements into account. The system, which gives a passer a rating between zero and 158.3, has its detractors. But it most often seems to confirm what knowledgeable observers say about which quarterbacks are playing well and which aren't, and this season it affirms that many of the sport's biggest stars are putting on dazzling displays. ...

"I don't necessarily love the passer rating system as a measure of quarterback play," Hasselbeck said. "If a guy is sacked and fumbled, that doesn't show up in the rating. But there are obviously a number of guys playing well, and that's reflected in the numbers. ...

"There are probably 15 to 17 guys where if you were running a team you'd say, 'I definitely feel comfortable building my franchise around this guy in any system. We can get to the Super Bowl with this guy as our quarterback,' " Hasselbeck, now an NFL analyst for ESPN, said by telephone this week. "I do think that's an unusually high number, to think that half the league or over half the league is comfortable with its quarterback situation."

The productive passing seems to be benefiting the teams involved and the league as a whole. The combined record of the clubs with quarterbacks who have passer ratings above 100 is 37-8. The league, meanwhile, has seen its television ratings soar this season; they're up 13 percent over last season and were at a 20-year high five weeks into the season. The sport's rules-makers always have considered a wide-open style of play attractive to fans.

"The ratings have been incredible," Colts owner Jim Irsay said last week at an NFL owners' meeting in Boston. "You really have to understand the sort of numbers we've been able to put up. That's been incredible and it shouldn't be understated."