ATHENS — Pass defense quietly has played a major role in who wins the national title.

During the Southeastern Conference's run of six consecutive championships, five of those champions ranked among the top two teams in the conference and the top four teams nationwide in pass efficiency defense.

The run-first SEC isn't known for throwing the ball all over the field, though that is changing. But SEC quarterbacks are effective when they do throw.

South Carolina's Connor Shaw and Alabama's A.J. McCarron are two of the nation's most efficient passers, and they could end up meeting in the SEC championship game.

Who wins the matchup — or even the chances of such a matchup occurring — likely depends on how well their respective teams defend the pass.

"I've always said I thought the thing that's different about this league was the pass rushers and the cover guys," Alabama coach Nick Saban said. "The combination of those things was a little better than other places. Everybody's got good receivers. Everybody's got good runners. There are lots of good quarterbacks. But I thought those two things were something that was a little better in this league."

There's no doubt SEC quarterback play has improved this year.

McCarron, Texas A&M's Johnny Manziel and Georgia's Aaron Murray all rank among the nation's top 16 quarterbacks in passing efficiency. Shaw would rank second nationally in that category, but he's one pass attempt shy of qualifying.

Even so, the conference race often comes down to which team has the best pass defense. Of the last six national champions that all came from the SEC, the only one that didn't finish among the nation's top four teams in pass efficiency defense was the Cam Newton-led 2010 Auburn squad that ranked ninth in the SEC and 76th nationally in that category.

That trend is unlikely to change this year.

Alabama topped the nation in pass efficiency defense while winning the national title last year and leads that category again this season. Just behind Alabama are Florida and LSU. Last year, the SEC had the nation's top four teams in pass efficiency defense: Alabama, South Carolina, LSU and Georgia.

Part of the reason for that dominance is because the SEC annually features some of the nation's top pass rushers. Even the SEC's own defensive backs are quick to credit their linemen.

"They do a great job of pressuring the passer, which makes the quarterback make quicker decisions than he wants to (and) maybe throws a bad ball every once in a while," LSU safety Eric Reid said. "I've caught a couple picks that seemed like punt returns just because of the quarterback trying to get the ball off (under duress). So a lot of the credit - most of it - can probably go to the d-line."

But the SEC also has produced plenty of NFL defensive backs during this dynasty.

The SEC had each of the last three winners of the Jim Thorpe Award given annually to the nation's top defensive back: Tennessee's Eric Berry in 2009, LSU's Patrick Peterson in 2010 and LSU's Morris Claiborne in 2011. Eight defensive backs from the SEC - the most of any conference - have been drafted in the first round over the last three years.

"Everybody in the SEC has athletes - especially in the secondary," Mississippi State cornerback Johnthan Banks said. "All the teams are so athletic on offense, you've got to have guys who can match up, guys who can play anywhere on the field. That's what you've got to have in this league so you can be ready for anything."

In the most recent draft, Claiborne, Alabama safety Mark Barron, South Carolina cornerback Stephon Gilmore and Alabama cornerback Dre Kirkpatrick were selected among the first 17 overall picks. LSU had to replace cornerback Tyrann Mathieu, a 2011 Heisman Trophy finalist removed from the Tigers' 2012 roster for a violation of team rules.

Even after losing all those stars, the SEC still boasts some of the nation's best defensive backs. Alabama cornerback Dee Milliner, Reid and Banks are regarded as potential first-round draft picks.

"I really think you're going to get a lot of bigger, stronger, quicker DBs in the SEC," Georgia linebacker Christian Robinson said. "Not that there's not guys like that in the other conferences, but there's going to be bigger numbers in the SEC. I think the type of receivers you go against on your own team is a factor. We had A.J. Green here pushing guys like (former star cornerback Brandon) Boykin."

The connection between pass efficiency defense and SEC championships might seem odd for what's generally a run-oriented league. Of the 14 teams in the SEC this year, only Arkansas, Kentucky and Tennessee have attempted more passes than carries. Overall, 30 percent of the Football Bowl Subdivision teams throw the ball more than they run it.

Although most SEC teams prefer to run the ball, this league does feature plenty of quality quarterbacks. The SEC has come a long way since last year, when the league didn't have anyone ranked among the nation's 20 most efficient passers. Tennessee coach Derek Dooley calls it "probably as experienced and talented a group as they've had in the league in a while."

The list of SEC quarterbacks includes at least three probable early-round draft picks in Arkansas' Tyler Wilson, Tennessee's Tyler Bray and Georgia's Aaron Murray. But the quarterbacks enjoying the most team success don't throw nearly as often as those guys. This is one league in which it isn't a backhanded compliment to refer to a quarterback as a game manager.

Shaw averages fewer than 15 passes per game, but he completes more than three-quarters of his attempts. McCarron has thrown 12 touchdown passes without an interception. The SEC's other two unbeaten quarterbacks are Florida's Jeff Driskel and Mississippi State's Tyler Russell, who have been picked off just once each.

In the SEC, it's nice for a quarterback to be prolific, but it's better that he be efficient.

And those defenses that do the best job of limiting that efficiency often end up celebrating in January.