LATROBE, Pa. -- The Pittsburgh Steelers did not wear pads on the first day of camp, but the running backs didn't need contact to look the part Sunday as the team opened camp at Saint Vincent College.

Le'Veon Bell looked noticeably explosive. He says he's in the best shape of his life, and he's not lying.

Stutter steps. Change-of-pace runs. Straight-line speed. Watching Bell run is like one big tease for the Steelers, who can't play him until Week 4 because of his marijuana suspension. Bell's right knee injury, which kept him out of a playoff loss to Baltimore, still needs additional pre-practice stretching and isn't completely the same as the left one. But this is the best Bell has felt in a while, he said. If he had to play today, he could.

That might be why Mike Tomlin is challenging free agent signing DeAngelo Williams by saying Bell will run with the first team, even though Williams needs enough to work to be ready to start Week 1 against New England.

That won't be an issue if the first practice is any indication, Williams said. He "absolutely" got enough work as the backup because the offense ran dozens of plays throughout the day. Williams even commented on his feet hurting after the session.

"I don’t think there is any special emphasis on me getting any more or less carries," Williams said. "It goes by the scope of the day. And I don’t expect anything to be different (from today)."

Williams met Tomlin's challenge to drop below 220 pounds, closer to his listed playing weight of 215. Williams indicated Sunday that he's done that.

"I actually look better than minicamp and OTAs," Williams said.

Bell settled his marijuana case back in February, yet the Steelers don't know whether Bell's appeal with the NFL has legs, or even has a hearing date. Bell maintains he has "no idea." What seems certain is Bell will miss the Patriots game. But even if the league reduces the suspension, the Steelers need more convincing running from Williams like they got Sunday.

"He’s a power running back," center Maurkice Pouncey said of Williams. "He runs like himself. He doesn’t try to copy anybody else. You can really appreciate that from a running back. He’ll get those extra yards.”

The Steelers offense showed that it can get creative in its running attack, as it used Martavis Bryant on a reverse a few times on Day 1.

In other Steelers news, outside linebacker James Harrison and safety Will Allen did not practice. Harrison did conditioning off to the side. Both are expected back soon.