Caldwell was the Ravens offensive coordinator for about a year and a half. He took over from Cam Cameron late in the 2012 season and was credited as one of the main reasons the Ravens caught fire and won the Super Bowl. The offense performed well under Caldwell in the playoffs, but it was a different story in 2013.
All of the struggles certainly can't be pinned on Caldwell, who was saddled with an offensive line that was banged up and lacking talent, as wellas starting a young, inexperienced center. The trade of Anquan Boldin and nearly season-long injury to Dennis Pitta only made matters worse. Throw in a heavier, injured Ray Rice and Caldwell's task of putting together a formidable offense was nearly impossible.
Caldwell will inherit a team with a lot of talent, especially on the offensive side, but one that is undisciplined and has had trouble living up to expectations. It will be interesting to see how he fares in Detroit and if he can finally tap into Matthew Stafford's potential and turn him into a consistently great quarterback.
The Ravens weren't all that keen on bringing Caldwell back as offensive coordinator, so this really turned out to be the perfect scenario. The Ravens once again saw an assistant move on to become a head coach elsewhere, which makes working in Baltimore that much more desireable for other coaches. It also allows the Ravens to now search for their next offensive coordinator, someone a bit more dynamic who could elevate the play of the entire unit.
Norv Turner is the name that immediately comes to mind, though he is still under contract with the Cleveland Browns despite the fact that they fired their head coach. The Browns seem hopeful that whoever they hire to be their next head coach will retain Turner, which is generally a terrible idea, which naturally makes it something the Browns would be apt to do.
The Ravens could also choose to promote from within, but that seems unlikely after the offense had such a disappointing season. John Harbaugh may be willing to consider promoting Juan Castillo if the external options don't pan out as hoped.