An on-track tangle between Mark Martin and Denny Hamlin triggered a seven-car accident Thursday that may set the tone for two weeks of ramped-up racing at Daytona International Speedway.

"Trust me, we're not finished," said Greg Biffle, who was involved in the wreck.

Jamie McMurray, Joey Logano, Kyle Busch and Clint Bowyer also were part of the melee, which happened halfway into the first practice for the Budweiser Shootout.

Martin was in front of Hamlin in a pack of cars when Hamlin hooked the rear of Martin's car. The contact turned Martin into the wall. Hamlin and Martin agreed that the wreck started because each driver anticipated the other doing something different.

"Ultimately, everyone's out there jockeying for position and everything to find out what their car can do," Hamlin said. "I mean, it's hairy out there for sure, and those things are going to happen whenever you're running that close and there's miscommunication, you're going to have guys running into each other."

Hamlin, Martin, Biffle, McMurray and Bowyer _ driving in place of Kevin Harvick, who missed practice because of flulike symptoms _ were forced into backup cars for the Saturday night exhibition race that kicks off Speedweeks.

"It's a huge disappointment," Martin said. "I feel for my team, to be down a car already. It's not a good way to start off Speedweeks. I was really happy with my car there and I wish that we wouldn't have torn it up."

It could be just the beginning.

Last month, NASCAR relaxed its rules on bump-drafting and gave drivers permission to be more aggressive on the track. When Hamlin hit Martin, he was being pushed hard from behind by Logano in a tight line of cars.

The relaxed rules could lead to more intense racing.

"Yeah, it's aggressive bump-drafting," Biffle said. "That's what we were looking for _ aggressive bump-drafting."

Then he added, perhaps sarcastically, "What are we, 20-30 minutes into practice? It's gonna be awesome."

The second practice offered more car carnage.

Juan Pablo Montoya turned Kurt Busch into the wall, sending him to the garage with all the others. Busch also went to a backup car.

In a draw Thursday night, Carl Edwards won the pole. Harvick took the second spot, and Brian Vickers was third.