No, Amon-Ra St. Brown isn't quitting football to hide a pot of gold ... he just looked like it on Thursday -- and it's all 'cause he lost a bet to his teammate!
The Detroit Lions star showed up to media availability dressed as if he were a new Lucky Charms spokesperson ... and when reporters asked why he was in the all-green garb, he told them it's because USC fell to Notre Dame in their rivalry game on Saturday.
"We made an agreement," the 23-year-old former Trojans star said of he and his teammate, ex-Notre Dame defensive lineman Julian Okwara.