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Over the past several seasons, the defenders who have led the NFL in sacks represented a virtual who's who of quarterback tormentors, players whose reputations for wreaking havoc and laying waste to even the most meticulously designed pass protection schemes were well documented.

Dwight Freeney. Michael Strahan. Jason Taylor. Those are names that strike fear into any quarterback who has experienced the heat they bring.

Through the first eight weeks of the 2005 campaign, though, the league's top sack men are more like a "who's he?" of pass-rushers.

Indianapolis end Robert Mathis is strictly a situational rusher, having started one game in his 39 regular-season appearances, rarely logging more than 20 snaps in any outing. Kyle Vanden Bosch of Tennessee entered the 2005 campaign having appeared in just six more games (35) than he had missed because of knee injuries during his four previous seasons. The résumé of San Francisco's Bryant Young includes four Pro Bowl appearances, but they all came when he was a 4-3 tackle and he's now playing end in a 3-4 front. Derrick Burgess of Oakland posted six sacks as a rookie with the Philadelphia Eagles in '01, then had as many surgeries as sacks (three) over the next three seasons.

But nearing the halfway point of the season, Mathis, Vanden Bosch and Young are tied for the NFL sack lead, with eight apiece, and Burgess trails them by just one quarterback takedown.

Of the NFL's top 10 sackers so far this season, only Freeney (2004) and Strahan (2001 and 2003) have ever previously led the league in sacks. Strahan, who holds the league record for sacks in a season with 22½ in 2001 (yes, the NFL still recognizes the dive that Brett Favre took for his buddy), is joined in the top 10 by four players who came into the season with fewer sacks than that in their careers. The goal of every pass-rusher is double-digit sacks, but Burgess and Vanden Bosch entered 2005 with nine and five career sacks, respectively.

While it might be sack-rilegious to contend that proven sack men such as Freeney aren't still formidable pass rushers, the 2005 season has certainly produced some new faces in the quarterback hit parade.

"I really don't know why," said Mathis, who defies all convention by playing end at 235 pounds, and who registered his first double-digit season last year, when he recorded 10½ sacks. "I'm just a role player, a special-teams guy and a [part-time] defensive lineman, that's all. I'm doing what I'm supposed to be doing."

A special teams guy! Yeah, that was Mathis' initial description of himself. Yet while it's true that his penchant for knocking quarterbacks off their perpendicular axes hasn't yet earned him a pass on the Colts' kick coverage units, the third-year veteran and former fifth-round draft choice from Alabama A&M has emerged as one of the league's premier situational performers.

You look at Mathis, who now has 18½ sacks in his last 23 games, and wonder how it is that Indianapolis, whose starting weakside linebacker, Cato June, is a former college safety, hasn't tried to convert him to the back line. Truth is, there have been brief but failed attempts, and by minimizing Mathis' snaps, the Colts are getting maximum production. Over the last two seasons, he and Freeney, the NFL sack champion in '04 and a dominant player who has faced many double- and triple-teams this year and still has six sacks, have emerged as the league's most feared pass-rush tandem.

"Playing against [right offensive tackles] who weigh maybe 100 pounds more than me, my basic [approach] is not to take on the whole man," Mathis explains. "If I can get to a tackle's outside shoulder, now I've cut him in half, and I can handle that. But I know people look at me, at just 235 pounds and making plays, and they think, like, 'That's just not supposed be to happening.' But it is."

Other top-10 sack leaders whose 2005 success isn't "supposed to be happening" include:

Kyle Vanden Bosch

Defensive End Tennessee Titans Profile

2005 SEASON STATISTICS Tot Ast Solo FF Sack Int 36 25 11 1 8 0

• Vanden Bosch: The league's latest player to find success after departing the Arizona Cardinals, who selected him in the second round of the 2001 draft, the five-year veteran missed all but three games of his rookie season after tearing two ligaments in his right knee. Then he was sidelined for the entire 2003 campaign when he tore the anterior cruciate ligament in his left knee during a preseason game. Arizona let him depart this spring as an unrestricted free agent, and Tennessee, seeking some veteran guidance for its young defensive end corps, signed Vanden Bosch to a one-year contract for the $540,000 minimum salary. Recommended to Tennessee officials by linebackers coach Dave McGinnis, his former head coach in Arizona, Vanden Bosch has been one of the season's biggest steals. "I'm healthy again and my confidence is back," he said. "I'm being counted on to make plays again." His eight sacks, which include a three-sack game against Baltimore on Sept. 18, are three more than he totaled in his first four seasons.

• Young: One of the NFL's premier 4-3 "under" tackles and one of the classiest performers during his first 11 years, Young was viewed by scouts over the last two seasons as a onetime great defender in decline. And there were serious doubts that he would be able to make the transition this year to end in the 3-4 scheme new head coach Mike Nolan installed. So far, with eight sacks, Young has proved the skeptics wrong. He was always a disruptive pass rusher from the interior (12 sacks in 1996, four double-digit sack seasons and 47 total sacks from 1996-2000) because he had the kind of natural leverage and slipperiness it takes to get to the quarterback from the inside. In a very short period, Young has been able to apply some of those same principles at left end, and has essentially resurrected his career. His eight sacks are more than he's registered since 2000 and just one fewer than he totaled in the previous three seasons.

Derrick Burgess

Defensive End Oakland Raiders Profile

2005 SEASON STATISTICS Tot Ast Solo FF Sack Int 22 20 2 0 7 0

• Burgess: After netting six sacks for the Philadelphia Eagles in his 2001 rookie season, the former third-round draft choice missed 31 games because of injuries over the ensuing two campaigns. In 2004, Burgess had as many sacks in the playoffs (three) as he did in the entire regular season. Credit Oakland personnel boss Michael Lombardi, one of the NFL's top talent evaluators and a guy who rarely gets cited for his acumen, for realizing Burgess' strong postseason performance last year might represent a career renaissance. Known to teammates as "Big Smooth," Burgess is becoming a big headache again to opposition left tackles. His seven sacks, including a string of three straight games with two sacks each, are a career high. Those seven sacks are also three more than the Philadelphia ends have totaled this season. Some people questioned the wisdom of the Raiders in signing Burgess to a five-year, $17.5 million contract as an unrestricted free agent this spring. Through eight weeks, that investment looks pretty good.

• Brian Urlacher, middle linebacker, Chicago: A household name, for sure, but not always a fixture in the opposing backfield, the six-year veteran has six sacks, already the most he has posted since 2001. After collecting 14 sacks during his first two seasons, Urlacher averaged only 4.2 sacks over the next three years, and his high in that stretch was 5½ sacks in 2004. Urlacher is not only coming up the middle on the blitz now, but coach Lovie Smith is moving him around some on third down and getting him more chances to rush the quarterback in general.

• Reggie Hayward, end, Jacksonville: The five-year veteran totaled just 11½ sacks during his first three seasons (2001-03), and then nearly equaled that in 2004, when he rang up 10½ sacks despite not even starting the season opener. Desperate for an upfield presence, the Jaguars signed Hayward as an unrestricted free agent this spring and, while there have been stretches of inconsistency, he has notched 5½ sacks in seven games.

Len Pasquarelli is a senior NFL writer for ESPN.com. To check out Len's chat archive, click here .