The preseason hasn't even started yet, and Pittsburgh Steelers wide receiver Antonio Brown is already upset with the referees. During a joint practice between the Steelers and Detroit Lions, Brown apparently made an acrobatic catch in the corner of the end zone. But the catch was ruled incomplete, which caused Brown to unleash a tirade at an official.

According to the Pittsburgh Tribune Review, Brown was upset referee Terry Brown ruled he was out of bounds after he caught a long pass from quarterback Landry Jones. Brown protested the call, and subsequently earned a personal foul. The referee vows to report Brown's conduct to NFL corporate offices.

“We're here to enforce the rules,” the official said afterwards, via the Tribune Review. “This is their practice. He will do it here and get away with it. But if he thinks he can do that and get away with it in a game, he's got another thing coming. I'm still going to report it to the league.”

It's difficult to envision Brown receiving anything more than a nominal fine for this transgression, but it's still noteworthy to see a player lash out at a referee during practice. It's a hallmark to Brown's intensity –– and perhaps lousy officiating as well.

No joke: Antonio Brown in the verge of being ejected... from a **preseason joint practice** for unsportsmanlike conduct toward an official — Chris Adamski (@C_AdamskiTrib) August 10, 2016

Thanks to commissioner Roger Goodell's "yellow card rule," which will mandate a players' automatic ejection after two personal fouls, referees may be proactive in policing on-field behavior this season. The rule will be reviewed after a trial run.

It's been a newsworthy training camp for Brown, who was in the headlines Tuesday for torching Lions cornerback Darius Slay during practice. "He tried to kill me, man," Slay said, via the Detroit Free Press.

The star wideout appears to be fired up this summer, which could be tied to his demands for a new contract. Though Brown reported to training camp on time, he said he wants to be rewarded for his recent string of 100-yard seasons. Brown, who's recorded an NFL-record 265 catches over the last two years, is due to make $6.25 million in base salary in 2016.

The Steelers and Brown's agent are reportedly talking contract, but no deal appears to be on the horizon.