Offensive stats:
Rushing - 18th in ypg, 16th in yards per rush.
Passing - 31st in ypg (only Rams are worse), 29th in sacks allowed.
Defensive stats:
vs Rushing - 20th in ypg.
vs Passing - 31st in ypg, 26th in QBR allowed, 18th in sacks.
The passing game is what is killing the 9ers. Being last vs the pass is a sure way to be giving up a lot of points which they are: 25.7 points per game allowed. Being last in passing is a sure way to be terrible in scoring which they are: 14.7 points per game. To give you an idea how bad 14.7 points per game is, the next team above them is the Rams offense at 18 points per game.
Matching up their weaknesses in the passing game, from Krapperdick's inability to read the field and the 9er OL's inability to pass block to the Rams' strengths in bringing the heat and mixing coverages/looks means an enormous advantage to the Rams in this matchup.
The only real positive in this matchup for the 9ers is their running game. It is respectable given the status of their passing game, and the Rams have struggled vs the rush from time to time. If there is a way to attack this Rams defense it is on the ground with a power run game. So the Rams defense will need to be on its game vs the run.
Offensively the Rams should be able to get Gurley going once again, I really don't see any issues with them gashing that front given that they've done it against the Cardinals. Then there's the passing game where the Rams' sorry passing attack should get healthier for at least this matchup.
This game is a pretty big mismatch in the Rams favor from where I'm sitting.