Change of possession. Alabama's 11 from offense run off the field. 15 defensive players run on. 15?
Yep. That's how Saban rolls.
Actually, there's logic behind this. He sends 15 out until they can see what personnel the offense is going to come out in. Once they see the offense's 11, Kirby Smart makes the defensive personnel call and 4 run off.
This article by Don Kausler (The Birmingham News) takes a look at how Saban's teams have evolved into playing entirely "Situational Defense". Plenty of good stuff in there about why Saban believes you have to focus on situations.
One nugget we gleaned is that Saban doesn't think defenses should huddle anymore. Saban, "...I used to coach getting in the huddle and breaking the huddle...Now, even when we're not playing against a no-huddle team all of our guys stand out there like in no huddle. But really, it has to be that way, because if you make them get in a huddle all the time and you play against a no-huddle team, they want to all go stand in a huddle."