RICHMOND, Va. – After seven months and 28 races, NASCAR has hit the part of the season that really matters. The start of the playoffs signifies a shift in attitude and aggression, and if there was any doubt the mindset had changed, Kevin Harvick posted a warning about his mood for the next 10 weeks.

It was a video of an angry bull charging into the grandstands.

And so the Chase for the Sprint Cup championship begins Sunday at Chicagoland Speedway with 16 drivers focused on the big prize. It’s 10 races with three rounds of elimination.

Don’t be surprised if tempers boil over, paint is traded on the track, angry words are exchanged. It’s already started to a degree. Tony Stewart has intentionally wrecked drivers in two consecutive races, including Saturday night’s regular-season finale with contact that ended Ryan Newman’s shot at making the Chase.

A frustrated Newman called his former boss “bipolar” and said Stewart had anger issues. Stewart was nonchalant, said Newman had it coming after running into him three times.

The Chase and this format can bring out the worst in even the most mild-mannered driver. Matt Kenseth tackled Brad Keselowski in a very un-Kenseth-like attack in 2014, then earned a suspension last year for an intentional crash that ruined Joey Logano’s title chances.

Denny Hamlin, who won Saturday night to give Joe Gibbs Racing three consecutive victories at Richmond and wins in nine of the last 15, said the jockeying for the final spots in the Chase field led to some of the recent aggression. He also speculated the length of the season could be a contributor, especially for drivers not contending for the title.

“Some guys have a care factor that’s really low right now,” Hamlin said. “I think things get a little bit tamer in the Chase because people are aware of the Chase cars. Whether they say so or not, they definitely race a little bit more careful around those guys, especially when you’re not racing for a win.”

As for the Chase drivers? Hamlin expects to see tense racing.

“As guys get eliminated, it could definitely ramp back up again,” he said.

Harvick, the 2014 champion and the first winner under the elimination format, has never backed down. His scathing assessment of his pit crew led to two changes to his team last week. When he was flagged for speeding on pit road, driver error instead of team error, it could have been seen as a bit of karma working against Harvick for being less than politically correct about his own crew.

He doesn’t care what it takes, though. He just wants results.

“You just have to be selfish. You have to do what’s best for your team, not worry about the consequences,” he said. “You have to be narrow-minded, not listen to anything.”