Mark Geragos says he knows "beyond a shadow of a doubt" the NFL blackballed his client Colin Kaepernick ... and it's entirely because of Donald Trump.
Kap's attorney -- who's reppin' the former QB in his collusion case against the league -- revealed some of the ammo he's usin' to prove his case on Amy Dash's podcast Tuesday ... and he says it all starts and ends with Trump's disdain for anthem protests.
"[We] got an owner under penalty of perjury testifying that he changed his mind after he was told what Trump said," Geragos said.