MINNEAPOLIS -- Their best players were Pro Bowl snubs last year. They have no outspoken stars like Richard Sherman, no catchy nickname like the "Legion of Boom." And the only time they've been on national TV this year was a game they'd probably rather forget about.

The Minnesota Vikings' defense doesn't come with much fanfare, and the group doesn't seem to ask for much of it. That could change soon enough, however -- because the Vikings' defense has become one of the best in the league.

Just two years after allowing a league-worst 480 points, the Vikings have given up the second-fewest points in the NFL, allowing just 154 through nine games. (The unit with the fewest points allowed, the Cincinnati Bengals, is the group Vikings coach Mike Zimmer led before he came to Minnesota.)

The Vikings are the only team in the league not to allow at least 24 points in a game this season. They allowed their first 300-yard passer when Derek Carr racked up garbage-time yards to get to 302 on Sunday, and they've only let one running back go over 100 yards since Carlos Hyde gashed them for 168 in their Monday Night Football season opener. And because of the defense (and Adrian Peterson), the Vikings are 7-2, leading the NFC North before a pivotal game against the Green Bay Packers this Sunday.

So why has the group been so good? Here are five things to know about the Vikings' defense:

Vikings safety Harrison Smith has proven to be one of the NFL's heaviest hitters -- just ask the Bears' Matt Forte. Jonathan Daniel/Getty Images

1. They've got one of the league's best safeties: Harrison Smith didn't make the Pro Bowl last year, and wasn't even the first alternate. But he put up the numbers to go last year as the Vikings turned him loose, becoming the only player in the league with three sacks and at least three interceptions (he finished with five, tied for third in the league). This season, Smith has a sack, a forced fumble and an interception, and he's made a habit of lighting up skill-position players with clean, but vicious hits. He sidelined Matt Forte with an open-field tackle two weeks ago in Chicago, and decked Amari Cooper on Sunday, putting his shoulder into Cooper so fiercely that officials called a personal foul penalty before realizing Smith hadn't done anything wrong. "It doesn’t hurt -- unless it’s the receiver," Zimmer said. "We want our guys to be physical and give them a good shot but we’re always trying to play fair and hitting them in the target zone. You know, Harrison’s a big guy, and he’s physical and tough, and he’s going to get some of those shots."

2. Their coach has the admiration of Peyton Manning and Aaron Rodgers: Zimmer's scheme is predicated on heady players who know how their responsibility affects the rest of the defense, and while his players never seem to end the year with gaudy stats, his defenses are usually near the top of the league. In 16 years as a coordinator or head coach, Zimmer has led eight defenses ranked in the top 10 in yards (including this year's Vikings) and six ranked in the top 10 in points. That's despite finishing in the top 10 in takeaways just three times. Zimmer might not have invented the double-A gap blitz, where two linebackers walk up on either side of the center, but he's mastered it, throwing in corner and safety blitzes off the pre-snap look to keep offensive lines guessing. Earlier this year, Manning called Zimmer a "founder of the type of defense he runs," adding the Broncos refer to the scheme as the "Mike Zimmer defense" when they see it around the league. And last year, Rodgers called Zimmer a "great football mind," after a Packers offense that had scored 50 points in back-to-back games managed just 207 passing yards in a win over the Vikings.

3. They get off the field: The Vikings are tied for third in the league in third-down defense, allowing opponents to convert just 32.2 percent of the time on third downs. They rank just behind the Rams at 32 percent. And in the red zone, the Vikings are almost as good. They're fourth in the league (just behind the Bengals), allowing a touchdown only 44 percent of the time.

4. They don't give up big plays: Opponents have managed only 28 plays of 20 yards or more against the Vikings this season, which is the third fewest in the league behind the Broncos and Buccaneers. The Vikings' blitz packages have forced quarterbacks to unload quickly -- teams are throwing in an average of just 2.38 seconds, according to ESPN Stats & Information -- and they've mostly neutralized deep threats like Calvin Johnson, Alshon Jeffery and Cooper. This defense isn't plagued by as many broken coverages as the Vikings' units of recent years, and the group tackles well enough to stop many explosive plays before they start. Todd Gurley, who had seven runs of 20 yards or more in his first five games, didn't manage anything longer than 16 yards against the Vikings.

5. They have a dominant nose tackle: When the Vikings signed Linval Joseph to a five-year, $31.25 million deal in March 2014, it seemed like a sensible signing that filled a need for their defense. But now that Joseph is in his second year in the system, having moved beyond an uneven 2014 season that began with him missing the preseason after getting hit in the leg by a stray bullet in a nightclub incident, he's turned into a force. He was named the NFC Defensive Player of the Week after recording 10 tackles (three for loss) and a sack against the Rams, and he followed it up with eight tackles and a sack on Sunday against the Raiders. Zimmer has said Joseph might be the best nose tackle he's ever had, and the 27-year-old is putting together a Pro Bowl bid. "He’s been very, very physical. He’s starting to get a lot more double-teams now obviously because of the way he plays," Zimmer said. "He does an awful lot of dirty work and doesn’t necessarily get the recognition -- I know he’s getting more now. He doesn’t really care about getting recognition, I don’t believe. He just wants to win and help his buddies to play good and keep linebackers free and if he falls into a sack here or there, he’s excited about it."