From N.T.A.:

Several people were injured Saturday night after they were splashed with a caustic substance believed to be some type of acid during a fight. It happened just after 9 p.m. on Oak Street near 17th Street.

Metro fire, police, and HazMat crews responded to the scene, where at least six to seven people had chemical burns. One victim had second degree burns.

“The reports are that someone stopped, got out of the car, and slung from some kind of a squirt bottle some type of liquid on the crowd,” said Major Richard Albers with Louisville Fire & Rescue.

One person received second degree burns.

Police are investigating, but so far there have been no arrests.

Anyone with information is asked to call the crime tipline at 574-LMPD (574-5673).

Sounds like drain cleaner to me, but the substance is as of yet unidentified.