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 19 card in Wheeling, West Virginia.
LET'S GET ROWDY!!!
"I guess they f***ing hated each other since their playing days, baseball," Portnoy said Wednesday.