It's called "shell drill" and when it's time to do it, the Colorado women's basketball players know they need to get serious.

"That's one of the hardest drills and you have to focus and pay attention in that drill and if you don't, uh, then you most likely won't be playing," junior guard Brittany Wilson.

Shell drill is a 5-on-5 half-court defensive drill against the male students that the Buffs practice with.

"Each guy is someone on the opposing team and we just guard them the way we're going to guard in the game," Wilson sad. "(Head coach Linda Lappe) stresses that a lot, being ready when we have to do that part. When we get in the game, it seems to be clicking."

Colorado (15-2, 4-2 Pac-12) has vaulted to No. 20 in the latest Associated Press poll, in large part because its defense has become a nuisance to the opposition.

Entering Friday night's game against No. 7 California, CU is allowing just 52.4 points per game, which is on pace to shatter the school record. The 1996-97 team allowed 56.8 per game.

CU has the No. 1 defense in the Pac-12 and has allowed just 48.2 points per game in its six conference games. The Buffs rank 24th nationally in scoring defense.

"For us, defense is one of the top things on that list that we take pride in," sophomore Jasmine Sborov said. "We see it kind of sets the tone for Colorado basketball. Coach Lappe loves defense and she's taught us to love defense. We've come a long way from last year.

"We've all learned to love defense and we know that's what is going to get us where we want to go."

Lappe was known as a stellar defender when she played at CU from 1998-2003, so it's no surprise she brought a defensive mindset to the Buffs when she was hired as their head coach before the 2010-11 season.

CU’s Brittany Wilson guards New Mexico’s Bryce Owens earlier this season. Wilson is often tasked with defending the best player on the opposing
CU's Brittany Wilson guards New Mexico's Bryce Owens earlier this season. Wilson is often tasked with defending the best player on the opposing team. ( CLIFF GRASSMICK )

In her first season, Lappe's Buffs allowed 62.6 points per game. They cut that to 58.4 a year ago. This season, they've dropped that number by another six points per game. Meanwhile, the offense is posting 68.5 -- up from 60.7 a year ago -- because the defense creates so many more scoring opportunities.

"It's taken three years and I think we've finally got the hang of it now," Wilson said. "We see that if we defend, they can't score and ... it gives us more confidence because we're pushing on transition off the defensive plays. I think it energizes our team."

CU has yet to allow 70 points to an opponent this season -- the deepest the Buffs have ever gone into a season without yielding 70. The Buffs have held eight consecutive opponents under 60 points, including Cal (53 on Jan. 6) and No. 6 Stanford (57 on Jan. 4).

Of the five different opponents CU has faced in Pac-12 play so far, four of them scored their season-low point total against the Buffs. That includes Arizona State and Arizona, which combined for just 79 points during CU's two wins last weekend.

"I really honestly do think it's a reputation that we're setting for ourselves," Sborov said. "You can tell how different teams run their offenses against us, just to adjust to our defense. You can tell they are definitely scouting it, which is good."

Wilson has become CU's stopper. She has routinely taken on the task of shutting down the opponents' best guard. She held Louisville's Shoni Schimmel to four points, Cal's Layshia Clarendon to five and Arizona's Davellyn Whyte to 11 (although nine of those came in the first few minutes of the game, before Lappe put Wilson on her).

"She has emerged as our best defender and she takes a lot of pride in that," Lappe said. "Two years ago, I probably wouldn't have ever thought I would say that, but she understands that's a role of hers and she understands that our team needs that. She wants to guard the other team's best player and she has confidence in that."

Wilson isn't alone. Junior center Rachel Hargis has had her best games against teams with quality post players. Senior point guard Chucky Jeffery is a top-notch defender, as well. And, then there's sophomore Lexy Kresl, who may be the best example of how the Buffs have gained a defense-first mentality.

Kresl came to the Buffs last year as a sharp-shooter from 3-point range. While she can still be deadly from beyond the arc, Kresl has developed into a confident defender, as well.

"She's expanded her game," Lappe said. "Now she understands the importance of defense."

All the Buffs have developed that understanding, which is why they're a top-20 team with eyes on the NCAA Tournament.

"We know if we can play really solid defense against really good teams, we can beat them," Sborov said.

That's why the shell drill, and any other defensive drill used by CU coaches, won't be going away any time soon.

"Our players work extremely hard defensively," Lappe said. "They work hard at it in practice and it carries over to the games. I'm pleased with where our defense is. Defense can win you a lot of games."

Follow Brian on Twitter: @BrianHowell33.

CU women's hoops preview

FRIDAY: The No. 20 Colorado Buffaloes (15-2, 4-2 Pac-12) visit the No. 7 California Golden Bears (15-2, 5-1) in a 9 p.m. game at Haas Pavilion in Berkeley, Calif.

BROADCAST: TV -- Pac-12 Network, with Krista Blunk on play-by-play and Mary Murphy with color commentary. Radio -- KKZN (760 AM), with Mike Rice on play-by-play and Carol Callan providing color commentary.

STORY LINES: CU has the longest current winning streak in the Pac-12, at four games. ... The Buffs' last loss came on Jan. 6 against Cal in Boulder, 53-49. ... CU's only losses this year have come against No. 6 Stanford and No. 7 Cal; Cal's only losses have come against No. 4 Duke and No. 6 Stanford. ... This is CU's fourth game against a ranked opponent this year; the Buffs are 1-2 against ranked opponents. Cal is facing a ranked opponent for the fifth time in its past six games; the Bears are 4-2 this season against ranked opponents. ... CU is 4-0 away from Boulder this season. ... Cal has the No. 1 scoring offense in the Pac-12 (72.2 points per game), while Colorado has the No. 1 scoring defense (52.4). ... CU ranks No. 4 in scoring (68.5) and Cal is No. 4 in scoring defense (56.8). ... CU leads the conference in rebounding defense, allowing just 31.6 rebounds per game. Cal is No. 2, at 32.3. ... CU's Chucky Jeffery has averaged 15.7 points and 8.7 rebounds per game in Pac-12 games this season.

KEY STAT: Colorado is 14-0 this season when it out-rebounds its opponents, and the Buffs have the second-best rebounding margin in the Pac-12, at plus-11.7. California, however, leads the conference, at plus-11.9, and the Bears have out-rebounded the Buffs in all four meetings since the start of last season.

COACHES: Linda Lappe is 54-32 in her third season at CU and 104-68 overall. Lindsay Gottlieb is 41-12 in her second season at Cal and 97-51 in her career.

PROBABLE STARTERS: Colorado -- G Chucky Jeffery, 5-10, Sr. (13.5 ppg, 8.4 rpg, 4.3 apg); G Brittany Wilson, 5-7, Jr. (7.9 ppg, 2.5 rpg, 2.5 apg); G Lexy Kresl, 5-11, So. (6.1 ppg, 2.6 rpg); F Arielle Roberson, 6-1, Fr. (13.6 ppg, 5.8 rpg); C Rachel Hargis, 6-4, Jr. (5.4 ppg, 3.2 rpg). California -- G Brittany Boyd, 5-9, So. (13.3 ppg, 4.4 rpg); G Layshia Clarendon, 5-9, Sr. (14.6 ppg, 4.1 rpg); G Afure Jemerigbe, 6-0, Jr. (6.9 ppg, 2.8 rpg); F Gennifer Brandon, 6-2, Jr. (12.6 ppg, 11.4 rpg); C Talia Caldwell, 6-3, Sr. (8.8 ppg, 6.5 rpg).

SERIES: CU leads the overall series 5-4, but Cal is 4-0 against the Buffs since CU joined the Pac-12 Conference last season.

UP NEXT: CU will visit No. 6 Stanford on Sunday at 5 p.m.