Second-year pro Kadeem Edwards took the first-team snaps in Monday's practice, the first in pads. Marpet, a second-round draft pick, worked with the second and third teams.
But don't read too much into that. The Bucs are hoping that Marpet will emerge as the starter as camp and the preseason go on.
"We don't have time periods on making those decisions," coach Lovie Smith said. "When it's obvious what we should do or when it's obvious that someone has moved ahead and they're definitely the starter, then we go with it. It's going to be a while though."
For now at least, Marpet is competing against Edwards and Garrett Gilkey. But the Bucs like the quickness of Marpet and aren't worried about the competition he played against at Division III Hobart College.
Marpet caught Smith's eye in a good way in one-on-one drills.
"I know I saw his first rep going against a pretty good football player in Henry Melton and he more than held his own," Smith said. "I think Ali will see that 'I can do this and I'm quick enough to handle this.'"
Marpet said the speed of the defensive linemen is the biggest difference as he adjusts to the NFL.
"It's a big difference because, in college, when we would do one-on-ones we'd only go against our scout guys," Marpet said. "Here, the third deep guys are still freaks. Going against them is what gets you better. We'll be doing one-on-ones every day. It's hard not to get better when you're doing that."
There's a lot of training camp left for Marpet to improve and climb the depth chart.
"It's a big transition," Marpet said. "Ideally, I'd like to be starting the first game. But if the coaches don't think I'm ready for that, then it's their call."