PITTSBURGH — Pittsburgh Steelers quarterback Ben Roethlisberger will miss tonight's game at Baltimore because of a concussion, an unforeseen development that forces the inexperienced Dennis Dixon to start one of the Super Bowl champions' biggest games this season.

Dixon, the former Oregon star, has spent most of the season as the No. 3 quarterback running the Steelers' scout team during practice. He has thrown only one NFL pass in two seasons, but must play because both Roethlisberger and backup Charlie Batch were hurt during a 27-24 overtime loss to Kansas City last week.

Roethlisberger practiced all week despite sustaining his fourth concussion since 2006. On Thursday, during his only interview of the week, he said he had been cleared to play, joking he passed "thousands of tests."

Roethlisberger, however, experienced headaches resulting from the concussion — his knee struck the knee of Chiefs linebacker Derrick Johnson as he leaned headfirst during the first play in overtime — and he began debating the wisdom of playing after consulting with the team's medical staff.

The Steelers decided yesterday that Roethlisberger will play only in an emergency. He will be the No. 3 quarterback, with former Pitt starter Tyler Palko — who was signed only Thursday — as Dixon's backup.

FoxSports.com first reported that Roethlisberger would not play.

The Steelers (6-4), losers of their last two, are a game behind Cincinnati (7-3) in the AFC North. The game plan for the Ravens (5-5) was built around Roethlisberger playing.

HALL OF FAME

RICE, EMMITT ON SEMIFINAL LIST OF 25

Jerry Rice and Emmitt Smith are among 25 semifinalists for the Pro Football Hall of Fame.

Former Raiders receiver Tim Brown and Cardinals and Rams defensive back Aeneas Williams were the only other players selected in their first year of eligibility.

Rice and Smith hold some of the NFL's biggest records. Smith is the league's all-time leading rusher with 18,355 yards for the Cowboys and Cardinals from 1990-2004. Rice is the all-time leading receiver with 1,549 catches for 22,895 yards with the 49ers, Raiders and Seahawks from 1985-2004.

The list will be reduced to 15 by Jan. 7. Dick LeBeau and Floyd Little have already been selected as finalists by the Seniors Committee.