Colts bench Trent Richardson

— -- INDIANAPOLIS -- Colts running back Trent Richardson has gone from being the biggest trade acquisition during the season to the bench.

Richardson is being replaced in the starting lineup by Donald Brown for Sunday's game against the Tennessee Titans, a source confirmed.

Richardson, who the Colts acquired from the Cleveland Browns for a first-round pick in September, had been expected to be one of the team's cornerstones with quarterback Andrew Luck.

But Richardson, the No. 3 pick in the 2012 draft, has struggled the entire season.

He is only averaging 2.9 yards a carry and has yet to rush for more than 60 yards in a game this season.

The Colts are trying to jump start an offense that has been outscored 93-12 in the first half of the past four games.

Brown opened the season as the third-string running back but he's been the team's most consistent back this season. He had 80 yards and two touchdowns against the Titans on Nov. 14.

NFL Network had earlier reported Richardson's demotion.