Although the overall numbers have started to stabilize, Tom Brady — along with Drew Brees and Aaron Rodgers — remains on pace to break Dan Marino’s 27-year-old record for passing yards in a season. (Winslow Townson/Associated Press)

This NFL season began with quarterbacks and receivers making defenses look more overmatched than ever before. They spent four weeks piling up passing yards at the fastest rate in history and leaving open the question of whether the league’s rule-makers had virtually legislated good defense right out of the sport.

But just when the competitive balance between passing offenses and passing defenses seemed to be tilted overwhelmingly in favor of quarterbacks and receivers, defenses have made a modest comeback. The passing assault has slowed a bit over the past five weeks.

This still could be a season in which significant portions of the record book are rewritten. Offenses could set league-wide single-season records for passing yards and scoring. Three quarterbacks — New England’s Tom Brady, Drew Brees of New Orleans and Green Bay’s Aaron Rodgers — are on pace to break Dan Marino’s 27-year-old NFL record for passing yards in a season.

But defenders at least are putting up a fight again, leading some observers to conclude that defenses are steadying themselves after taking longer than pass-first offenses to recover from the offseason inactivity wrought by the NFL lockout.

“The way the season started, with all those huge passing numbers, proved that the group that was affected most was the defense,” Steve Mariucci, the former coach of the San Francisco 49ers and Detroit Lions who now is an analyst for the NFL Network, said recently. “There were a multitude of blown coverages. I think you’ll see that slow down. I think we’ve even started to see that. . . . You see people starting to run the ball a little better. I think that’s what we’re going to settle into.”

The season started with a passing deluge. Brady totaled 940 passing yards in the season’s first two weeks. Carolina Panthers rookie quarterback Cam Newton began his NFL career with a 422-yard passing game followed by a 432-yard effort.

The first four weeks of the season produced the top four league-wide passing-yardage totals in NFL history. The average game in the season’s first four weeks yielded 491.3 net passing yards (passing yards minus yards lost on sacks).

In the past five weeks, though, defenses have managed to reduce that figure to 446 net passing yards per game. Individual quarterbacks have managed only two games with 400 or more passing yards in the last five weeks, one by the New York Giants’ Eli Manning and one by Houston’s Matt Schaub, both in Week 5. That’s after quarterbacks had eight games with at least 400 passing yards in the season’s opening four weeks, including two each by Brady and Newton and one apiece by Brees, Rodgers, Philadelphia’s Michael Vick and Miami’s Chad Henne.

“The first four weeks of the season were the equivalent of training camp,” former Washington Redskins quarterback Joe Theismann said recently. “Now, for me, we’re finally into the season. I think defenses will catch up to offenses. The runners will start to run the ball more effectively. We’re back to a normal season.”

If so, it’s part of what veteran broadcaster Matt Millen, a former NFL player and executive, described earlier this season as the sport’s “new normal.” The league-wide totals of 5,795 points and 60,880 net passing yards (prior to Oakland’s Week 10 victory Thursday night at San Diego) are the most ever through nine weeks of an NFL season.

There have been only two 5,000-yard passing seasons in league history. Marino threw for a record 5,084 yards for the Dolphins in 1984 and Brees threw for 5,069 yards for the Saints three years ago.

This season, there could be at least three more. Brady, Brees and Rodgers are on course to break Marino’s record and San Diego’s Philip Rivers is just shy of a 4,900-yard pace. Newton and Eli Manning are on pace to top 4,700 yards each. Newton seems likely to shatter Peyton Manning’s rookie record of 3,739 passing yards for the Indianapolis Colts in 1998.

But in recent weeks, defenses have stiffened. Analysts say they no longer see as many receivers left totally uncovered because of missed assignments in the secondary.

Some teams also have turned to backups at quarterback, not always with the best results. In Week 7, a combination of benchings and injuries resulted in six new starters, headlined by Denver turning to Tim Tebow, Minnesota going with rookie Christian Ponder and the Redskins starting John Beck ahead of Rex Grossman.

Ponder and Beck haven’t managed a 300-yard passing game between them but have topped 200 passing yards in each of their starts. Tebow has yet to have a 200-yard game, totaling 457 passing yards in his three starts as he was sacked 15 times.

Offenses have turned more to their running games as the season has progressed. The average game in the last five weeks has included 243.6 rushing yards, up from 217.1 in the season’s first four weeks. Scoring is down a bit, to 43.6 points per game from 45.6 in the first four weeks.

Atlanta Falcons President Rich McKay, chairman of the NFL’s competition committee, said he suspected all along that defenses would find ways to catch up as the season progressed.

“You are seeing awfully good quarterback play,” McKay said in a recent telephone interview. “For a rookie to come into the league and be near the top of the league in passing yards [Newton ranks sixth], that’s very rare. I was certainly surprised early in the season. It didn’t feel like a normal year, with all of the passing.

“But I’ve been around long enough to know those things tend to stabilize. Defenses tend to find a way to solve some of those issues. You tend to see the running game become more prominent, and everything tends to kind of sort itself out.”

Rule changes over the last decade have contributed greatly to this being the most passing-friendly era in NFL history. The competition committee told officials to crack down on illegal contact by defensive backs on receivers more than five yards downfield prior to the 2004 season. More recently, there have been safety-related rule changes that restrict hits on quarterbacks and receivers in vulnerable positions.

But McKay said he never thought, even in the first four weeks of the season, that there would have to be future rule adjustments to aid defenses.

“Defenses tend to find a way to move themselves into a better place to compete with offenses,” he said. “Offenses tend to need help from the rules at times to counteract certain defensive strategies.”