A joint Lebanese security force was called to the university Tuesday afternoon after the fight, which injured seven students and the head of campus security, students told The Daily Star.
Soldiers remained on the scene as classes resumed Wednesday.
Students said at least two students were hospitalized with injuries from the fight between supporters of former Prime Minister Saad Hariri's Future Movement and supporters of Speaker Nabih Berri's Amal Movement.
A professor said Ahmad Hassouna, head of the LAU's security unit, sustained a head injury after being struck by a helmet.
Witnesses said the fight started after Amal supporters shouted slogans as a Future Movement convoy drove past the university's upper gate playing songs in celebration of Hariri's birthday.