Two NFL clubs that looked all but certain to make the playoffs this season, the San Diego Chargers and Pittsburgh Steelers, haven’t been getting much out of a star player lately -- and both teams are struggling. Each is looking for a turnaround when they square off in Pittsburgh Sunday, and the statistical intrigue makes this showdown the NFL Matchup of the Week.

Chargers RB LaDainian Tomlinson has just two 100-yard games in a frustrating season, during which the team has gravitated to the success of QB Philip Rivers and the passing game. Tomlinson has rushed for less than 75 yards in five of nine contests. He’s been held to less than 50 yards on the ground in three of San Diego’s five losses.

Since upending New England on Oct. 12, the 4-5 Chargers have lost two of three games and barely escaped with a 20-19 win over the 1-8 Chiefs last week. The challenge Sunday for Tomlinson and the Chargers, who trail the 5-4 Broncos in the AFC West, is getting the franchise’s first regular-season win in Pittsburgh.

The Chargers are 0-12 all-time playing on the Steelers’ home field in the regular season. Making the 13th matchup the lucky first win would mark a big step toward a serious playoff push for the Chargers, who need to turn their season around soon.

In losing two of their last three games -- a tough stretch in which Pittsburgh won at Washington and lost home contests to the Giants and Colts -- Steelers QB Ben Roethlisberger has thrown for just one touchdown and been intercepted eight times. The quarterback is giving no indication how much he is he bothered by a sore shoulder, the result of an injury suffered early in November.

Roethlisberger gets a chance to kick-start the passing game Sunday. San Diego’s pass defense is among the worst in the league. The team holds down one of the three lowest spots among NFL clubs in opposition completion percentage (67.8%), opponent passing yards per game (264.9) and opponent passing touchdowns (17). Only the Arizona Cardinals have allowed more passing TDs (18). No team has given up more passing yards per game than San Diego.

The Chargers defense also has the NFL’s longest active streak by failing to intercept 128 consecutive passes. The pick-prone Roethlisberger, with eight in his last three games, may be catching a break.

The Chargers offense has been slow-starting for much of 2008, but has recovered to tally 139 second-half points, tied for the second most in the league. That presents a challenge for the Pittsburgh defense, which has given up just 64 second-half points, the third fewest among all teams. Chargers QB Rivers leads the NFL with 21 touchdown passes, including 11 after halftime. Will the 6-3 Steelers be able to shut down San Diego’s passing game to the very end?

The Steelers defense has been especially successful against the pass. It has allowed only 171.1 passing yards per game in 2008, the fewest in the league, and ranks first with 34 sacks. Pittsburgh is third in fewest points allowed per game (15.6).

If the Chargers could treat the game with the urgency of a playoff matchup, pulling out that first regular-season win in Pittsburgh is a more realistic possibility. After all, in the only two postseason games between the two teams in Pittsburgh, the Chargers won both times.