Dave Portnoy Says Pat Mahomes Sr., John Rocker Will Box At Rough 'N' Rowdy

We saw this coming from a mile away -- Patrick Mahomes Sr. and John Rocker will face off in a boxing match ... with Barstool Sports founder Dave Portnoy announcing the two former MLBers have signed contracts to fight at Rough 'N' Rowdy.

El Pres shared the news minutes ago ... saying the "Beef on Bourbon Street" will headline his April 18 card in Wheeling, West Virginia.

"I guess they f***ing hated each other since their playing days, baseball," Portnoy said Wednesday. "I mean, I guess not surprising. Everyone has beef with John Rocker."

"But they signed the f***ing paperwork," he continued ... adding the bout ain't gonna be like Jake Paul vs. Mike Tyson -- 'cause there's real bad blood between the two.

Portnoy also took shots at the three-time Super Bowl MVP ... saying he's well aware of how the Kansas City Chiefs superstar hates Barstool, and he's gloating a bit.

"Well, now your dad's fighting in our company against John Rocker. So I'll save a seat. Free of charge."

Of course, RNR is amateur fighting ... with randos signing up to beat each other up for pure entertainment purposes. So it's far from Ali vs. Frazier.

As we previously reported, footage made rounds on Tuesday ... showing 54-year-old Mahomes Sr. and Rocker, 50, getting in a heated confrontation on Bourbon Street during Super Bowl week.

It looked staged ... especially after Portnoy said a fight between the two was in the works.

Unclear if the confrontation was manufactured to generate hype for the fight or if the two really do hate each other's guts like that ... But Portnoy is adamant it wasn't.

"It's honestly insane to insinuate that we would stage a fight on Bourban Street to promote a fight that was announced a couple days later," he said.