Mike Tomlin's smile slipped into a smirk. During breakfast at the NFL owners meeting, we were discussing the league's inexorable shift toward the passing game. A longtime defensive assistant before joining the Pittsburgh Steelers in 2007, Tomlin refused to concede.

"There will always be [a counter]," he said. "It was amazing a few years ago that we sat in here and we talked about the Wildcat. Ohhh, the Wiiiiiildcat. I bet no one has a Wildcat question today, because there is a counterpunch defensively. That's the awesome thing about football. There are guys in labs right now, like [Steelers defensive coordinator] Dick LeBeau, working on that and responding to things."

Yes, the Wildcat formation proved more a gimmick than a game-changer. And Tomlin spoke with the confidence of a coach whose pass defense ranked No. 1 in the NFL last season.

But on the whole, can NFL defenses counter an advantage that has been decades in the making? Is there anything that can stop a trend that produced a trio of 5,000-yard passers in 2011 -- including the Detroit Lions' Matthew Stafford -- and has, as the chart shows, resulted in steadily rising passer efficiency over the past 25 years?

ESPN.com's NFL bloggers explored the topic with more than a dozen coaches and general managers this offseason. Few shared Tomlin's confidence, describing instead a weighted fight against offenses that boast advantages in both rules and personnel. They connected the rise of the passing game with the NFL's apex in popularity, suggesting the league has ample motivation to ensure offensive supremacy.

"You're not going to stop them," an NFC executive said. "The league is built around prolific offenses. We're never going back to the days of a team scoring in single digits. Let's face the facts. The rules just are very much in favor of the offenses."

Defenses, of course, will continue trying. A team that can consistently limit opposing passers is a sure bet for a deep playoff run. That alone is worth the effort. So let's take a closer look at the issue and then inspect the NFL's current defensive thinking on it.

A long time coming

As the chart accompanying this post demonstrates, this shift is not a recent development but rather a steady climb. Since the 1987 season, gross passing yards and attempts have increased by 25 percent. A portion of that rise can be attributed to franchise expansion, but the climb of passer efficiency -- via the NFL's passer rating system -- illustrates how teams are experiencing substantively better success when they throw.

The 2010 and 2011 seasons, in fact, marked the first times in NFL history when the combined passer rating of all league quarterbacks exceeded 84.

Coaches and executives we spoke with boiled down the causes to three major factors: bigger receivers, rules limiting contact 5 yards beyond the line of scrimmage and newly enforced emphases on contact to the head and quarterback hits.

Defenses now have to contend with bigger receivers and faster tight ends -- like Rob Gronkowski. AP Photo/Charles Krupa

"The development of quarterbacks and receivers in recent years," said Atlanta Falcons coach Mike Smith, "have made it hard to match up and eliminate or neutralize the strength of those guys. You've got athletes to beat man coverage and formations to beat zone coverage. I don't really see that changing."

New Indianapolis Colts coach Chuck Pagano, a former defensive coordinator for the Baltimore Ravens, sinks a little further in his seat every year at the NFL scouting combine.

"You go there and you're trying to find cover corners to match up with these guys," Pagano said, "and every year these receivers are getting bigger. They walk across the stage and every time they call out the measurables, it's 6-foot-4, 6-5, 220 pounds, 230 pounds. Most of the corners are 5-8, 5-9, 5-10. It's becoming increasingly hard to find that 6-1 cornerback, and now that you have the rise of tight ends as well, you've got so many athletic guys that create matchup problems. It's tough to keep up."

The physical mismatch is exacerbated, coaches and executives say, by rules that limit defensive aggression and physicality.

"It's become hard because the rules have changed so much over time," Tennessee Titans coach Mike Munchak said. "There's limits to what the defensive players can do and guys are even thinking now about how and whether they can hit a receiver."

Green Bay Packers general manager Ted Thompson, whose team allowed an NFL-record 4,796 passing yards in 2011, is among those who understand the issue is not a recent development.

"Just looking at some of the statistics," Thompson said, "[passing] offense has been growing since the inception. I think it's just continuing. I do think the NFL is a very exciting game. My guess is the league itself likes that. It does make it harder to play the game of defense, though."

Thompson cautioned against assuming the game is simply in a cycle that will work itself out.

"There is a natural, 'Ok, you do this, now we'll do this,'" he said. "The people that play defense and coach defense are trying, but the league is a pretty high-powered thing right now."

What to do?

Based on our interviews, at least, it appears NFL teams are shifting their defensive priorities to compensate. Pass rush now dwarfs coverage in terms of importance, but teams are emphasizing coverage skills at supplementary positions more than ever, especially at linebacker and safety, in the draft.

"We can have all the DBs we want," said Houston Texans coach Gary Kubiak, "but if we can't make the quarterback get rid of the ball, it doesn't matter. So [it] starts with pass rush all the time."

Pagano, the coach who watches taller receivers arrive at the scouting combine every year, said: "I think you find that people are trying to put more pressure on the quarterback and not giving quarterbacks a chance to get comfortable in the pocket. People are trying to dictate the tempo. That's the biggest thing.

"Eventually everyone is going to try to find the guy on their team that can match up on the outside. They'll try to find at least one cover guy or a true cover guy. They'll say, 'Here's our No. 1 corner, go take out the best receiver that they've got.' Match him up that way. But I go back to trying to dictate the tempo of the game and getting pressure."

That, of course, is easier said than done. Elite pass-rushers are among the NFL's rarest commodities, leaving many teams to devise elaborate blitz packages to compensate.

"Defenses have to find a way to get pressure on the quarterback with only four pass-rushers," an NFC executive said. "If you're sending linebackers or defensive backs as blitzers, you're going to get torn apart."

Chiefs coach Romeo Crennel says teams need to have linebackers and safeties who can cover. John Rieger/US Presswire

That's true especially when facing elite or near-elite quarterbacks who understand the vulnerabilities of various blitz packages. So what's the answer? For obvious reasons, coaches were loath to discuss schematic solutions, but Kansas City coach Romeo Crennel added some context for how a successful 2012 pass-first defense could be deployed.

A competitive defense in this era, Crennel said, must employ above-average coverage skills at most, if not all, of the seven of the linebacker/defensive back positions. They must work in tandem with a pass rush that doesn't need more than five players to put pressure on opposing quarterbacks.

"You have to be able to cover," Crennel said. "You’ve got to have guys that can cover. So you're looking at corners that can cover, linebackers that can cover and even safeties that can cover. And not only zone safeties but safeties that can go man-to-man. Because you have to be able to mix man in there.

"So I think that’s the biggest thing, particularly the linebackers, because in the formations the linebackers are going to have to walk out and cover a tight end or a back that's out of the backfield, and if they can’t move and they can't cover, offensively they find that matchup they like right now and they go right at it.

"So I think you see defenses transitioning from being those run-stopping defenses where you put eight guys in the box to spreading things out, matchups, doubling more receivers, and then those linebackers have to be able to cover. Because if they can't cover, they're going to get isolated."

Therein lies another problem. How many NFL linebackers can be counted on to cover receivers or even the newest generation of tight ends? There aren't enough to go around, that's for sure.

In the end, a handful of teams could assemble enough players with coverage skills and match it with an active pass rush to give quarterbacks more fits than most opponents. But can anything curtail the larger trend? NFL coaches and executives cast serious doubt on that question. One compared the current combination of factors to the impact of baseball lowering its pitching mound in 1969 to boost batting averages.

In many ways, what's done is done.

"The league doesn't want to curtail it," Buffalo Bills coach Chan Gailey said. "I don't get the feeling that's the case at all. I think the more scoring, the more exciting plays, the better. I don't see it going the other way for a while."