The Dolphins are a mediocre team. Not bad, not real good. Tua won't change that. Fitz was playing really well for them. I can't imagine that Tua is somehow going to improve them. The switch can only be about next year and beyond, with the FO and HC realizing that they aren't going anywhere this year so they may as well get him some experience.
Rams are dealing with a few injuries, but nothing they don't have the depth to overcome. The D is really coming on, is lights out in the 2nd half of games, and the O is clicking pretty well (they have yet to play to their potential). The good news is that the Oline remains intact (hope I didn't just jinx them) and is performing well. They can beat you up with the run, and overwhelm you with the pass.
So the wheels would have to fall off (ala the Niners first half) in order for them to lose the game.
