I agree with Petersen. Shaq was the best player on the field every time he lined up at RB. Which is really saying something, given his lack of experience at the position.
Is Shaq and an NFL RB? That is debatable. But in college, he clicked at RB in a big way. His style was reminiscent of David Wilson, who was linear and stiff but otherwise outstanding, setting records at Virginia Tech. Wilson bombed in the NFL for the Giants, though Coughlin's old school nature played a big role in that.
Shaq has the tools to be a Jeron Johnson type at safety. As a LB, I think he's a better version of Mason Foster. If the big plays go away, he'd be nondescript. The selling point would have to be that the big plays aren't going anywhere. Honey Badger is the comp Shaq will want GMs to make. Shaq will earn money with big plays, not by being the glue of a defense.