Someone caught up with Usher ... and sued him for allegedly stealing a huge hit.
Three guys claim they wrote a song, "Caught Up" back in 2002. It's about a man lost in love.
Usher recorded a song 2 years later called "Caught Up" ... also about a man lost in love. It skyrocketed on the charts and was featured in his album, "Confessions."
The 3 guys -- Zacharia Edwards, Mitch Moses and Vince McClean -- claim they played it for a honcho at Arista Records -- Usher's label -- and the dude then played it for LA Reid. The 3 guys never heard from Arista again, but 2 years later they heard the song on the radio.
They're suing for unspecified damages.