Pittsburgh Steelers rookie quarterback Dennis Dixon will make his first start on Sunday night. Pittsburgh Steelers rookie quarterback Dennis Dixon will make his first start on Sunday night. (Keith Srakocic/Associated Press)

Steelers quarterback Ben Roethlisberger will miss Sunday night's game at Baltimore because of a concussion, an unforeseen development that forces the inexperienced Dennis Dixon to make his first NFL start.

Dixon, a former University of 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 practised all week despite sustaining his fourth concussion since 2006. His head struck the knee of Chiefs linebacker Derrick Johnson as he leaned headfirst during a running play in overtime.

During his only interview of the week, Roethlisberger said Thursday he had been cleared to play. But he continued experiencing headaches resulting from the concussion and began debating the wisdom of playing.

The Steelers were so convinced Roethlisberger would play, they did not sign an experienced quarterback even after Batch broke his left wrist a few plays after replacing Roethlisberger Sunday. Batch will miss most or all of the rest of the regular season.

While Roethlisberger went through a usual Wednesday practice and with Batch out of the picture, second-year pivot Dixon took more snaps than usual. Dixon was selected in the fifth round of the 2008 NFL entry draft.

Roethlisberger's decision to not play comes in the same week the NFL has taken a heightened stance on protecting players from head injuries.

The Steelers decided Saturday 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 and doesn't know the offence — as Dixon's backup.

The Steelers likely will rely mostly on running backs Rashard Mendenhall and Willie Parker and limit the amount of throws Dixon makes.