There’s an old saying in football that a good offense sells tickets but a good defense wins championships. If this is true, then championships start on the defensive line. Whether a team is playing a 3-4 scheme or the more popular 4-3 defense, it’s the guys up front who set the tone for everything the defense does.

If the linemen can’t generate a strong pass rush, the defensive backs have to maintain their coverage longer, and big plays ensue. Likewise, if the guys up front are getting pushed off the line of scrimmage, their opponents will gain yards on the ground.

An exceptional defensive line can help cover for weaknesses in other areas, but if the line isn’t playing well, the whole defense will struggle.

Take the Tennessee Titans, who lost two key players from a defense that ranked no. 1 against the run last year. The departure of Jevon Kearse and Robaire Smith has left them with a much less potent line, as has been evidenced by their surrendering an average of 153 rushing yards over their last three games. It’s one of the main reasons why a team that was 12-4 last year has started 1-3.

The Vikings have also struggled against the run, and their inability to get pressure on the quarterback is making life miserable for their defensive backs. Minnesota’s opponents pass the ball on nearly two-thirds of their plays (64.1%) because they know they’ll have time to throw. When the Vikings try to increase the pressure by blitzing, a player like LB Chris Claiborne or CB Brian Williams has to come out of coverage, making for a catch-22.

The job of individual linemen vary from team to team. Ideally, a defensive end has the size and strength to stuff the run and the speed to get into the backfield and pressure the quarterback. But you can count on one hand the number of guys in the NFL who have that combination of talents: New England’s Richard Seymour, Miami’s Jason Taylor, the Giants’ Michael Strahan, and the Colts’ Dwight Freeney.

While offensive lines tend to use the five players in every situation, defenses often employ specialists – ends who play only against the run, or pass-rushing specialists who enter the game in passing situations.

Teams that play the 4-3 defense typically employ a good run stopper on the strong side (near the tight end) and a pass rusher on the weak side. In the 3-4 package, both ends must be good against the run, and the pass rush typically comes from an outside linebacker.

Defensive tackles also come in two varieties. There are the 1-gap tackles, defenders whose job is to penetrate the gaps between offensive linemen. These guys tend to be smaller, but they have speed and explosive power.

Players Like Oakland’s Warren Sapp and Philadelphia’s Corey Simon make big plays by getting into the backfield or disrupting the blocking, making them effective weapons against both the run and the pass.

A 2-gap tackle doesn’t penetrate; his job is to occupy blockers and take up space. This clogs running lanes and keeps blockers off the linebackers, who are then free to make plays. Buffalo’s Sam Adams and Detroit’s Shaun Rogers are probably the best 2-gap tackles playing today. Their massive size makes them tough to move, but it’s their strength and explosive quickness that make it hard for opponents to control the line of scrimmage.

No matter how good the individual linemen are, however, they have to play well collectively in order for the line to succeed. The conventional wisdom is that the Panthers’ front four of Julius Peppers, Mark Rucker, Kris Jenkins, and Brenston Buckner is the most talented in the league. That may be so, but the numbers suggest they haven’t been particularly dominating this year. They’re 13th in the league in allowing 3.87 yards per running play, and 18th in registering a sack for every 15.8 pass plays.

It should not come as a surprise that some defensive lines play very well in one phase of the game but struggle in the other. Jacksonville’s run defense has been stifling, and they have two of the game’s best defensive tackles in Marcus Stroud and John Henderson. Yet they only had 24 sacks last year (29th in the NFL) and are on pace to have even fewer this year. The Patriots, by contrast, have been relentless in their harassment of opposing quarterbacks, but have been below average against the run.

The NFC’s three undefeated teams sport prime examples of defensive lines that are doing both well. Atlanta’s defense was horrible last year, but this year they rank second against the run and second in sacks. The addition of DT Rod Coleman has helped free up ends Patrick Kerney and Brady Smith to bring pressure from the outside. It has also allowed linebacker Keith Brooking to take better advantage of his speed and make more plays.

Much of the attention in Philadelphia has focused on the impact of WR Terrell Owens, but one of the big reasons the Eagles are undefeated is their defense. The unit ranks sixth against the run and leads the NFL with 18 sacks. That’s nearly half of their 2003 total in just four games. The two veteran defensive ends they added through free agency – Kearse and Hugh Douglas – have been consistently disruptive.

Grant Wistrom has had the same kind of impact in Seattle. The defensive end has helped the Seahawks line stiffen against the run and made them one of the most aggressive pass rushing units in the league. In three games, Seattle opponents have scored a total of 13 points, and the improved play of the line is a big reason.

The Seahawks and Falcons are looking like strong Super Bowl contenders, in large part due to their defensive play. The Eagles have fallen one game short of the Super Bowl for three straight seasons, and their improved pass rush might make 2004 the year they finally reach the big game.