"It's not about the fact that they all came from Bama, it's the fact that all these Bama backs have (mostly) not been used properly. Bama's offenses is basically a carbon copy of the Texans/Seahawks/Redskins offense. It's all zone runs, lots of PA boots thrown in with deep shots to Amari Cooper (and Julio Jones back in the day). For a running back, reading zone blocking is way, way different than reading power. In a zone scheme the reads are often protracted and take more time since any one of three or four different holes could open up over the course of one run.
For instance, on a zone stretch the primary read might be a 5-tech defensive end. If his offensive tackle executes a successful "reach block" and seals the edge, then he races to the corner and tries to turn up field. If the defensive end beats the tackle to his outside shoulder, then his read suddenly becomes off the guard and center (depending on the alignment of the defensive front). Again, he's reading to see if the defenders are on the right or the left of their blockers. Because of the lateral motion of the run, defenders can't really "two gap" like they normally would against a north-south power run scheme. Either they contain play side, or pursue back side, not both. The back reads which linemen win, which linemen lose, and makes his decision based off of that. The read takes longer, but if you have a back that can do it they can be deadly. Often this vision is what makes or breaks a one cut zone runner rather than athletic ability (case in point Arian Foster and Alfred Morris).
Now, on a power scheme the back is often reading one designed hole that the play is intending to get the ball through from start to finish. It's a faster read, and more often than not the back has to follow a full back or pulling lineman into the hole and react based on whatever chaos gets created in the wash. Power runners are often more athletically gifts (or just flat out bigger humans) because they have to bounce, juke, and pound their way through a mass of bodies that usually ends up in different places than initially planned. A lot of pure zone runners either lack the instinct or lack the physical ability to succeed in power schemes because it's a completely different style of read. Similarly, a lot of pure power runners fail in zone schemes because they lack the vision to dissect multiple blocks at the same time and make a decision to cut up field at the appropriate time (think Darren McFadden failing miserably last season when the Raiders switched to a zone scheme).
So what does this have to do with Bama backs? Indy runs power, Green Bay runs zone. Trent Richardson's bruising reputation in college caused him to get labeled as a "down hill power runner" coming into the league, but in reality he was just a one cut zone runner that also happened to be really, REALLY hard to tackle. He's basically Marshawn Lynch 2.0, except Lynch also happens to be in a zone scheme where his talents and vision can flourish with his ability to fight for yardage. Cleveland ran power, found out quickly that he wasn't a power runner, and traded him to Indy, who is now also finding out that he has no idea what he's doing in a power scheme.
Contrast all this with Lacy, who is in a scheme that runs lots of stretches, lots of pin and pull zone plays to the edge, and lots of tosses in order to get into situations where he is most successful - in space. Lacy thrives when he has time to read his blocking, so the Packers cater to that by using a lot of run plays that take longer to develop than the Iso's and Dives that come with most power run games. Will the Pack run a power play every now and then to take advantage of Lacy's size? Absolutely, but their bread and butter is letting Lacy read zone blocking and use his size and power to break tackles in space. Lacy is a very similar back to Trent Richardson. Both of them are big, powerful runners. The only difference is that one team is trying to fit a square peg in a round hole, while the other is not.
amn it Donald is now gone
