In the first half, the Titans offense was humming aside from a fumble on the one-yard line by every Titans fan's least running back Shonn Greene. However the Titans offense looked terrible in the second half and it is really hard to figure out why, but I think there are some clear reasons that Mettenberger struggled.
Despite Taylor Lewan keeping his edge of the pocket clean, the Titans other four offensive linemen struggled to keep defenders out of Mettenberger's lap. With no where to step into, it made it really hard for the Titans to spread the ball around which led to the Titans receivers being rendered ineffective.
The Titans receivers have been worse than expected this season, and for the most part the defenders were really staying tight. Mett had to throw some passes into tight windows, and often had to fit passes in on the sideline. Mettenberger can throw with anticipation, but with no where to step up and receivers not beating their defenders, a lot of passes ended up going to the running backs and tight ends.
Walker was having another good game, but a questionably legal blow to the head, Walker was forced out of the game. With his safety blanket gone, Mettenberger had a hard time progressing through his reads.
All in all a lot of things went wrong for the Titans, and it doesn't help that the officials called a bad OPI call that led to a stalled drive and a lack of confidence. It also doesn't help that Whizenhunt stopped calling creative plays and didn't adjust to the interior pressure brought on the Ravens. The important thing is that Mettenberger did show some improvement and is taking steps in the right direction.