SANTA CLARA, Calif. — Mike Nolan refers to his version of the nickel defense as the Big Sub. The San Francisco coach's scheme is earning some less-flattering nicknames from fans who don't think the Big Sub is doing much to stop big plays.

With four defensive linemen and five defensive backs on the field for large portions of two recent games, the 49ers (2-2) look different from most NFL teams, even if Nolan insists the Big Sub isn't much of a departure from what every other team does to capitalize on matchups.

Nolan touts the Big Sub as a way to stop long-gaining plays, with five defensive backs available to blanket the opponents' receivers. With four defensive linemen on the field, Nolan figures, the scheme also should be strong against the run and adept at rushing the passer.

So far, the numbers don't reflect Nolan's faith. San Francisco is in the bottom half of the NFL in most defensive statistical categories, giving up 97 points and 335.8 yards per game in the process.

The Big Sub will get its biggest test Sunday against the New England Patriots, who spent their bye week thinking about ways to exploit the unusual strategy employed by a coach who once drew criticism as a coordinator for his vanilla schemes.

"It's all matchups, and everybody in the league does it," said Nolan, a defensive coordinator for four teams over 11 seasons before getting the top job in San Francisco. "If you stay in base (defense) when they go to three wide receivers, and you have a lot of confidence that (linebacker) Takeo Spikes can cover Wes Welker, then you try to do that. In our case, I would like to think we've got a better matchup maybe with a defensive back."

But the 4-2-5 San Francisco defense's supposed strengths have been problems in recent weeks. Each of the 49ers' first four opponents had success running the ball, from Edgerrin James' 100-yard game in the season opener to Deuce McAllister's rejuvenated performance in last week's loss at New Orleans.

And while Nolan touts the Big Sub's importance in preventing long-gaining plays, the Saints had four passes of at least 33 yards last week, and the Niners mustered almost no pass rush to help those extra defensive backs on the field.

It's enough to turn any football fan into an amateur assistant coach, trying to come up with a better use of San Francisco's high-priced defensive personnel.

"The disappointment (in New Orleans) had more to do with the explosive passes than anything else," Nolan said. "If you take those away, which you can't take away because it's reality ... it wasn't a scheme issue when we got beat on those things."

Nolan attributed each of those mistakes not to his scheme, but to poor technique by his defenders: an incorrect angle taken on the ball, a late reaction or a simple inability to knock away a pass.

"A lot of it was technique," said Spikes, who has taken over Jeff Ulbrich's spot at inside linebacker after just four games with his new club. "The other part was we were just trying to press and make plays, and you open yourself up in other areas where you normally don't have to worry."

Nolan spent much of the past three seasons touting a 3-4 defensive front, and the linemen he chose as the 49ers' personnel boss are shorter, heavier bruisers who excel at stopping the run.

With the offseason arrival of versatile defender Justin Smith, Nolan adapted his long-preferred defense to put Smith in multiple positions — sometimes seven different spots in the scheme, from pass-rushing end to zone-coverage linebacker — during every game. But when the 49ers are in the Big Sub, Smith is basically a defensive end, and his effectiveness hasn't been as obvious.

New England coach Bill Belichick has been watching, and he's more impressed than the 49ers' fans.

"This year, they're based primarily out of a four-man front with Justin Smith, which is understandable," he said. "He's been very productive, and I think it looks more like what (Nolan) did in Baltimore, when they had (Terrell) Suggs. Even though he was an outside linebacker, he really played down, almost like a fourth defensive lineman. That's what Justin is doing."

Notes: The Big Sub has reduced the role of LB Manny Lawson, who has barely played on defense — but that won't hurt the 49ers this week. Lawson is out for at least one game because of a strained hamstring. ... San Francisco made no additions to its injury report Thursday. RB Frank Gore, who sat out of practice Wednesday to rest, was back on the field.