If you took away the typical 50 - 70 yard run that the Rams have allowed in probably 2/3rds of their games, then their Run D looks SO much better in the stats column. Don't get me wrong; those long runs are real, not flukes, and shouldn't happen but they did because the Rams didn't cover their run gaps.
But this is why there seems to be such a disparity between pass D, run D, and overall D.