There were six starts at quarterback last season among the nine games the 5-foot-11, 195-pounder played in, as he split the signal-calling duties with Barry Brunetti and Zack Stoudt.
He's still in the offensive backfield, only now as a running back. And he's basically moved to the head of the class among a talented group that includes junior Jeff Scott, freshmen Jaylen Walton and I'Tavius Mathers, senior Devin Thomas, and sophomore Nicholas Parker.
Mackey said he just wants to play. It's obvious he's going to get to. Most likely a lot. He's made his mark this preseason and looks forward to Saturday's opener.
And it doesn't concern him if he's at the top of the depth chart or not.
"I don't really too much care about that," said the senior from Bastrop, La., and East Mississippi Community College, who redshirted his first season in Oxford in 2010. "I just come out here and practice, just work to get better."
And he's done that, so much so that first-year Rebel head coach Hugh Freeze speaks glowingly of how Mackey has gone about things and what he potentially can do to help his team and himself.
"Consistency. Toughness. Competitive spirit. He's got all those things," Freeze commented in his weekly Monday press conference. "I said when I got here I thought he could be a special player if he got his act together, off the field primarily. He seems to have done that to this point. I'm cautiously optimistic that will continue. He's one of my favorite kids on the team. I think he feels he's got something to prove. I'm looking forward to seeing him in action."
Mackey said he's gotten used to his new position and the pounding it can take being a running back. But he attributes going against the Rebel defense for getting him ready for the season.
"After a month of hitting all of them, Mike Marry, Aaron Garbutt, I think I'm pretty good for contact with any linebacker in the SEC now," he said. "All of them guys bring it every day. So I'm ready for it."
As for Mackey, it's like a second chance, with a new head coach and a new position. He's appreciative of the opportunity he's been given and wants to make it count.
"It's really like some relief off my shoulders," he said of getting what amounts to a fresh start. "I was like, yes, I've finally got a chance to do it right. Thank the Lord he gave me that chance. Now I'm doing the best I can at it."
He also feels good about things in regards to how his coaches feel about him. He likes the fact that they are pleased with him.
"I'm very happy. It's good to see them all smiling and saying ‘I like what you're doing with yourself now.' Changed my image. Senior year. Got to be a leader on the team," Mackey said.
The depth that has apparently surfaced at running back is a positive as well, since the offense Freeze and company have brought in is up-tempo and fast-paced. Mackey said the numbers there mean they can be more effective, in his opinion.
"If we get tired, we've still got those other guys," he said. "We'll be ready to go. So that's a lot of help."
Mackey admits he thinks from time to time what it would have been like for him to have made the move to running back earlier in his career.
"Sometimes I do think about it. As of right now, I'd probably be a little better (at running back)," said the 2008 Parade All-American in high school. "But it is what it is, and I'm making the best of it right now."
Mackey said with his experience and motivation, he's ready when called on. And that's to do whatever is needed.
"Anything coach wants me to do. It doesn't matter," he said. "I just want to help the team out. I'm excited. Finally it's here. I just want to go out there and help my teammates and just win ballgames. That's it. We're going to see Saturday if it's paid off for us."