Stanford is a mystery at the moment. It drew raves by beating then-No. 2 USC at home on Sept. 15, but questions arose when it lost 17-13 to unranked Washington in Seattle on Sept. 27. No one really knows how good Stanford is, and people are still trying to gauge how much the loss of Andrew Luck to the NFL has hurt the Cardinal. The chief issue is that Stanford has very little room for error now. The Cardinal defense has been outstanding, which allows the team to be in every game. But the Stanford offense has been so unproductive that the Cardinal seems destined to play a lot of tight, low-scoring games in which one or two defensive mistakes could cost Stanford the game. That's what happened against Washington, which is far from a great defensive team but still prevented the Cardinal offense from scoring in the second half. That put a lot of pressure on the Stanford defense to make stops, and a 61-yard touchdown run by the Huskies changed the momentum. Arizona ranks third in the Pac-12 in total offense, and the Wildcats have more offensive weapons than Washington, which ranks 11th in the Pac-12 in total offense. Arizona dual-threat quarterback Matt Scott fits new coach Rich Rodriguez's spread option offense, and that style will present problems for the Cardinal defense, which will be spread out more than it was in previous games. In any case, Stanford quarterback Josh Nunes has to be more efficient than he was against the Huskies, when he completed just 18-of-37 passes for 170 yards. Coach David Shaw has shown no inclination to replace Nunes with Brett Nottingham, who was Luck's backup last season, but another poor game by Nunes could change Shaw's thinking. Stanford simply has to be more productive on offense, and needs at least to get a few first downs to prevent Arizona from having numerous opportunities to score with its wide-open spread-option attack. "We have shown before we can play well in stretches, but we have to play a complete game," Shaw said. Arizona appears to be at least as good as Washington, and the game against the Wildcats could be pivotal because a second straight loss heading into the Oct. 13 road game against No. 9 Notre Dame could send Stanford's season sideways in a hurry. NOTES, QUOTES Stanford suffering from huge dropoff on offense --Stanford failed to score an offensive touchdown against Washington, the first time that has happened since 2007, which was Jim Harbaugh's first season as head coach. It never happened in Andrew Luck's three seasons as the Cardinal's starting quarterback. Stanford ranks 105th out of 120 FBS teams in total offense, and it ranks 103rd in pass efficiency. Last year, Stanford was eighth nationally in total offense and fifth in pass efficiency. --Stanford is 3-0 at home this season and has won 16 of its last 17 home games, losing only to Oregon last year. --Stanford has not lost consecutive games since 2009, although Arizona was the team that turned the trick three years ago, a week after Oregon State had defeated Stanford. --Stanford is ranked 18th in the Associated Press poll, the 37th consecutive week the Cardinal has been ranked. The Cardinal has been ranked every week since Sept. 5, 2010. A loss to Arizona probably would end that streak. --QB Josh Nunes generally has been given enough time to throw. He has been sacked just four times this season, which is the fewest in the Pac-12. Stanford allowed just 11 sacks last year, which ranked seventh in the nation, and yielded just six sacks in 2010, which was second in the country. SERIES HISTORY: Arizona leads 14-13 (last meeting, 2011, 37-10 Stanford). SCOUTING THE OFFENSE: The Cardinal offense has not been nearly as explosive as it was last season, which is not surprising with the loss of Andrew Luck. Stanford has not been getting the expected consistent gains from its ground game against defenses that are loading up against the run. TB Stepfan Taylor is tough and has averaged 103.3 yards per game, but the Cardinal has not been carving out big holes and does not seem to have the tailback depth that was expected. QB Josh Nunes has completed just 52 percent of his passes, and the passing game has not been productive. The big-play potential is limited by the fact that Stanford does not have much of an outside threat among its wide receivers, although TEs Zach Ertz and Levine Toilolo are excellent possession receivers and probably the best tight end tandem in the country. SCOUTING THE DEFENSE: The Cardinal defense has been outstanding, especially against the run. It ranks third in the nation in rushing defense, yielding just 65 yards per game on the ground, although it gave up a 61-yard touchdown run to Washington. Its front seven is among the best in the country, and its depth and talent at linebacker is unmatched. Stanford's pass defense has been better than expected. Stanford's defensive backs have covered receivers better than they did a year ago, but the Cardinal's best weapon against the pass is its pass rush. Stanford has 13 sacks, but that number is deceiving because the pass rush has been particularly effective the past two games and has caused opposing quarterbacks to hurry even when they are not sacked. QUOTE TO NOTE: "The first three weeks, he progressed every week. ... He threw four bad passes [against Washington], but a lot of his deep balls were perfect, some were caught, some weren't. ... For whatever reason, he took a step back this past game." -- Stanford coach David Shaw, on QB Josh Nunes STRATEGY AND PERSONNEL THIS WEEK'S GAME: Arizona at Stanford, Oct. 6 -- Stanford is 3-1, including 1-1 in the conference, after a 17-13 loss to Washington. Arizona is 3-2 and has lost two straight, including a 38-35 loss to Oregon State on Sept. 29. Stanford has won two straight against Arizona and four of its last five against the Wildcats. KEYS TO THE GAME: Stanford wants to control the game with its power running game, and if it can do so, the Arizona defense figures to get worn down over the course of the game and the Arizona offense will have limited opportunities to unleash its explosive attack. The Wildcats rank 11th in the Pac-12 against the run, and Oregon State had success running against Arizona in the Beavers' 38-35 victory on Sept. 29, so there is every reason to believe Stanford can run effectively against Arizona. QB Josh Nunes has to be more effective on third down than he's been in the past, and he needs to hit some passes early to show he can be a passing threat. But his success will depend largely on the Cardinal's ability to run the ball. Defensively, Stanford needs to prevent the big play and avoid mistakes against the Arizona's spread option. If it does that, it should have enough talent to prevent the Wildcats from scoring a lot of points. PLAYERS TO WATCH: OLBs Chase Thomas/Trent Murphy -- Thomas and Murphy have combined for 10.5 tackles for losses and 4.5 sacks, and they need to prevent Arizona from getting outside on the option and prevent QB Matt Scott from having time to run or throw as he chooses. TEs Levin Toilolo/Zach Ertz -- They have combined for 23 receptions, 389 receiving yards and two touchdowns. They have been the Cardinal's most reliable receivers, especially on third down. Ertz had a career-high 106 receiving yards against Washington. TB Stepfan Taylor -- Taylor has averaged 103.3 yards per game, and he has handled a larger percentage of the ball-carrying chores than he has in the past. He also has 14 receptions. QB Josh Nunes -- He is not Stanford's best player, but he is certainly its most important player. He has completed 52 percent of his passes and needs to improve on that for Stanford to be successful. ROSTER REPORT --TB Anthony Wilkerson is questionable for the UCLA game because of a lower leg injury. --FB Geoff Meinken is questionable with a knee injury. --S Jordan Richard ranks fourth nationally in passes defensed with 2.25 per game. That includes seven pass breakups and two interceptions.