The points per game statistics are misleading in regards to Bama's defense. They're looking only at the final score of games and automatically attributing every point the opponent scored to the defense... which is incorrect.
Bama's defense only gives up 6.5 PPG total (including the 3 points LSU scored in overtime on Nov. 5th) and only gives up 6.3 PPG in regulation.
For example, the final score of the Auburn game was 42-14. Auburn's offense didn't score a single point against Bama's defense. They were completely shut out.
Auburn got a touchdown by recovering an A.J. McCarron fumble in the endzone, and Onterrio McCalebb returned the kickoff to open the 2nd half back for the other touchdown. None of those points were given up by the defense.
Georgia Southern scored 21 points in a game that Bama didn't game plan for, but only 14 of those points were scored on the defense. The special teams gave up the other TD on a kickoff return.
The only reason Kent St. scored 7 points at all in the season opener was because McCarron threw an INT and Kent St. returned it all the way to the 3 yard line.
Alabama's defense literally ranks 1st in every statistical category there is. Not just rushing, passing, scoring and total defense. They also rank 1st in several other categories (3rd down conversion, QB rating against, YPA, YPC, red zone scoring, total TD's given up, etc., etc.)
Since the NCAA began keeping statistics in 1937, Bama's defense is only the 2nd to rank #1 in the 4 major categories (rushing, passing, scoring, and total defense). But the ONLY defense to also rank #1 in all the other categories as well.
I've seen some great defenses in college football in my time (almost 50 years), but I've never seen a defense this dominant.
I think in Alabama's last 2 games that were both shutouts by the defense (Auburn and LSU) the opposing offense has only crossed the 50 yardline twice.