It's all a question of whether or not Alabama plays to their ability. They have some crazy splits in terms of run defense for instance.
The overall story is kind of interesting, but basically we are seeing improved defense in the second half. Here's some insight into that:
"Georgia averaged 9.8 yards per carry in the 3rd quarter, averaging 8.6 yards per carry on the game through that point. In the 4th quarter? 8 carries for 12 yards, 1.5 yards per carry. And 10 of that came on one play with a wide receiver rushing"
Alabama stopped the run at some crucial points in that Georgia game, after getting gashed pretty much the entire game they suddenly started to stop the run later in the game. And they didn't just stop it, they crushed it. Then we have the Vanderbilt game, where they again were getting gashed.
The second half comes along and Alabama only lets Vanderbilt rush for 20 yards on 8 carries (not counting the sack which caused them to have nearly no rushing totals for the half). That's 2.5 per carry in the half, to go with that fourth quarter 1.5 per carry against Georgia. One key was Alabama was able to control the clock and keep their defense fresh.
So, this defense can stop the run, they just have to be dialed in. The past two games overall their second half defense has been stellar, only giving up 7 points. Mind you, that's against the #6 offense and the #16 offense, those are stats that even a Saban defense would be proud of.
Now, does this translate to Missouri and can they do it in the first half? I don't know, but I see it going one of two ways. Either this is like Vanderbilt last year, where Missouri controls the clock and Alabama can't stop them, and it basically turns into a shootout, or this looks like traditional Alabama football. If Missouri can't run on Alabama, and Alabama can maintain a balanced offense, if Alabama defends the run like they did late against Georgia and the second half against Vanderbilt, Missouri will be in trouble.