The Red Sox picked up left-hander Andrew Miller on Friday, acquiring him from the Marlins in exchange for lefty Dustin Richardson.

In Miller, the Red Sox get a once-highly-rated prospect who has struggled to live up to his potential in the early part of his Major League career.

As the No. 6 overall pick out of the University of North Carolina in 2006, Miller was a key piece -- along with center fielder Cameron Maybin -- in the December 2007 trade between the Marlins and Tigers, which sent Miguel Cabrera and Dontrelle Willis to Detroit.

But Miller, who eventually ran out of Minor League options with Florida, has struggled with his control, dealt with nagging injuries and hardly found consistency as a big leaguer.

He went a combined 14-21 with a 5.50 ERA and 5.1 walks per nine innings in his first four years in the Majors. Miller then spent most of the 2010 season in the Minors after a rough Spring Training, going 2-9 with a 5.35 ERA in 21 starts for Class A and Double-A before a late-August callup to the big leagues.

At the Major League level, he went 1-5 with an 8.54 ERA in nine games (seven starts) to finish out the season.

Richardson, originally a fifth-round Draft pick by the Red Sox in 2006, split time between Triple-A Pawtucket and the Major League club in 2010. The 26-year-old posted a 4.15 ERA in 26 relief appearances in the big leagues, and went 3-0 with a 2.66 ERA and two saves in 32 relief appearances for the PawSox.

In his Minor League career, Richardson -- who also appeared in three games with the Red Sox as a rookie in 2009 -- has gone 25-21 with a 3.95 ERA in 142 games (50 starts). The Kansas native posted a 2.29 strikeout-to-walk ratio in that span.