Aroma therapy

After USC routed Washington, 56-0, and then dropped two spots in the Bowl Championship Series standings, Coach Pete Carroll said the system for determining a national champion “stinks.” Times staff writer Gary Klein looks at some of the key issues and matchups when USC plays the last ranked team on its schedule in a game with Rose Bowl implications for both teams:

Click or pick

USC quarterback Mark Sanchez was highly efficient in the Trojans’ rout of winless Washington, but the Golden Bears offer a much greater challenge. Cal is tied for the national lead with 17 interceptions.

Sanchez’s decision making will be put to the test against a 3-4 scheme that often features eight players dropping into coverage. Safety Sean Cattouse and cornerback Syd’Quan Thompson have three interceptions apiece, though Cattouse is doubtful because of a concussion.

Coach Jeff Tedford said Cal would start senior Nate Longshore at quarterback. Sophomore Kevin Riley is probably a greater threat to USC because of his scrambling ability, but the native of Portland, Ore., suffered a concussion last week against Oregon.

Longshore started the last two games against USC, struggling in 2006 at the Coliseum but bringing the Golden Bears close last fall at Berkeley. He will be facing a defense that ranks first in the nation and has shut out three of its last four opponents. Will Harris will start again at safety for USC in place of injured Kevin Ellison.

Speed trap

Joe McKnight’s right big toe is apparently sound, so the game will feature some of the fastest running backs on the West Coast.

Cal’s Jahvid Best is averaging 105 yards rushing a game, second in the conference behind Oregon State’s Jacquizz Rodgers. The sophomore from Vallejo has scored touchdowns on runs of 80 and 86 yards this season. He also is tied for the team lead with 21 receptions.

Best did not practice Thursday because of a sore foot but is expected to play. Teammate Shane Vereen averages 69 yards rushing a game.

“Their running backs are electric,” USC offensive coordinator Steve Sarkisian said.

A USC defense ranked No. 5 nationally against the run will try to short-circuit the Bears.

McKnight’s return adds speed to a Trojans rushing attack that alternately has been led by junior Stafon Johnson and sophomore C.J. Gable.

Johnson starred two weeks ago against Arizona and Gable got his turn last week against Washington, breaking off a 50-yard run as part of a 108-yard, two-touchdown effort.

Cal is fourth in the conference in rushing defense.

Tackle box

USC’s linebacker corps, save for a September stumble against Oregon State, has lived up to its billing as one of the nation’s best. Seniors Rey Maualuga, Brian Cushing and Kaluka Maiava are first, second and third on the team in tackles.

Cal’s linebackers have not received the publicity, but the unit has been productive. Seniors Zack Follett, Anthony Felder and Worrell Williams and sophomore Mike Mohamed have thrived in the 3-4 scheme the Bears adopted this season. Cal ranks first in the conference in red-zone defense and second behind USC in third-down conversion defense.

Lining up

Nick Howell will start at right tackle again for a USC offensive line that has given up a conference-low nine sacks while paving the way for a rushing attack that ranks third in the Pac-10.

Senior center Alex Mack is the leader of a Cal offensive line that has given up only 13 sacks. Cal ranks fourth in the conference in rushing but has run for only 12 touchdowns.

USC is first in the Pac-10 against the run but seeks more production from senior defensive tackle Fili Moala.

Margin of error

Paced by its penchant for intercepting passes, the Bears are the top team in the Pac-10 in turnover margin at plus-8.

USC ranks right behind the Bears in the Pac-10 at plus-6.

By the numbers

*--* USC CATEGORY CAL 40.3 Scoring 36.3 7.1 Points given up 21.0 256.0 Passing off. 230.2 204.1 Rushing off. 171.8 460.1 Total offense 402.0 127.5 Passing def. 190.5 84.1 Rushing def. 109.5 211.6 Total defense 300.0 *--*

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gary.klein@latimes.com