Michael Lombardo: The Chargers lead the league in total offense and rank No. 4 in total defense, so the obvious answer is putrid play on special teams. San Diego gave up three long kick returns in the season-opner against the Kansas City Chiefs, including a 94-yard touchdown by Dexter McCluster, and gave up two kickoff return touchdowns to Leon Washington in the second half of last week's game.
Turnovers have also played a role. San Diego has turned the ball over 11 times through three games, including seven lost fumbles. RB Ryan Mathews has still not played a full game without fumbling the ball, a streak he hopes to snap on Sunday.
BW: Is Malcom Floyd a legitimate No.1 receiver and how do you see him matching up with CB Dominique Rodgers-Cromartie?
ML: No, Floyd is miscast as a No. 1 receiver. He doesn't gain a lot of separation; he doesn't threaten the middle of the field; and he struggles to hang onto the ball after a collision. Floyd is a big-play specialist and will have some chances against Rodgers-Cromartie, but San Diego is playing receiver-by-committee at the moment. Look for 2007 draft picks Legedu Naanee and Buster Davis to be prime targets Sunday.
BW: Is RB Ryan Mathews back to full strength and will he have a big day against the Cardinals' 31st-ranked run defense?
RB Ryan Mathews
The plan is to try to jump out to an early lead, force Derek Anderson into some bad decisions and then run the ball in the second half. If the chips fall that way, Mathews could be in line for the first 100-yard game of his career. But it should be noted the Chargers rarely make things that simple.
BW: Defensively, is Shawne Merriman anywhere near the player he used to be?
ML: No, Merriman is essentially worthless at this point. He will miss Sunday's game with a calf injury, which only matters because 2009 first-round pick Larry English (foot) is also out with an injury. Still, backup linebackers Antwan Applewhite and Jyles Tucker are at least as good as Merriman at this juncture, if not better.
BW: With Antonio Cromartie gone to the New York Jets, who will line up against Larry Fitzgerald as the top cornerback in San Diego?
ML: Quentin Jammer has been San Diego's top cornerback for a long time now; Cromartie just got more attention because of his penchant for making flashy plays. Jammer is an elite player who will spend the bulk of the game locked up with Arizona's biggest playmaker.
Jammer has his flaws -- he struggles to locate the ball in the air and he sometimes gets too physical with receivers, drawing penalties -- but he provides consistently tight coverage and is an excellent tackler. He may be forced to play special teams Sunday because of San Diego's inability to tackle a return man, so it will be interesting to see if that affects his performance on defense.
BW: As a must-win game for the Chargers, how can they let this one slip away and fall to 1-3?
ML: Firstly, this is not a must-win game for the Chargers. The only team ahead of them in the AFC West is the Kansas City Chiefs, whose 3-0 record is a fluke (I dare anyone to watch game tape on Matt Cassel and say with a straight face that the Chiefs are going to the playoffs).
Secondly, it is not difficult to envision the Chargers losing this game. It's still early in the season and Norv Turner is still the coach, so it would not be out of character at all if San Diego came out flat and laid an egg.
Michael Lombardo is a member of the Pro Football Writers of America and a long-time contributor to the Scout.com network. His analysis has been published by the NFL Network, Fox Sports and MySpace Sports. He has followed the Chargers for more than 15 years and covered the team since 2003. You can see more of his updates by following him on twitter.