Things got so intense between referees at a youth basketball game in Colorado that they ended up throwing punches in front of a bunch of kids ... and now police tell TMZ Sports they're investigating the melee.
The ugly scene, which was captured on video, went down during a 4th-grade boys hoops game -- Cherry Creek vs. Legend Blue -- over the weekend at the Gold Crown Field House in Lakewood, CO.
The clip clearly shows two referees square up on the court after some type of disagreement ... when one of the refs throws a massive right hook, knockin' down the other official.