The MLB All-Star Game might have become the site of a mass shooting this week ... had it not been for a hotel housekeeper, who tipped off cops to a huge collection of guns she found in one of the rooms.
Local reports say 4 individuals were arrested this weekend in Denver -- 3 men and a woman -- on illegal weapons charges after cops say they discovered an incredible cache of artillery in their rooms at the Maven Hotel ... just 2 blocks from Coors Field, where the All-Star events will take place this week.