According to the feds ... Foy was one of the "most violent" rioters, and allegedly hit police officers guarding the doors at least 10 times with the hockey stick, swung at them, hit them in the face and neck, then rallied other rioters before busting into the Capitol.
A federal judge denied Foy bond this week ... so, for now, he'll remain behind bars until trial.
Foy -- a former marine -- was arrested on Jan. 21 at his home, after the FBI reportedly tracked him down through his father's Facebook page. The bond hearing judge said the video strongly suggested Foy brought the hockey stick to use as a weapon.
Foy's lawyer argued the stick was intended to be used as a makeshift flag pole ... but that did not fly with the judge.