Barisal police's Deputy Commissioner Golam Rauf Khan said that the clash broke out at the Karnakatthi on the Barisal-Patukhali highway.
BU students blocked the road when a student was shoved off a bus over a dispute on fare, he said.
According to the police official, students hurled brickbats leaving at least two policemen injured.
The police then lobbed tear-gas shells, sound-grenades and fired rubber-bullets to disperse them.
At least ten people were injured in the clash and most of them have been taken to the Barisal Medical College Hospital (BMCH), according to Shafiul Islam, the general secretary of BU Teachers' Association.
Naim Uddin, a law student of BU, got on a local bus from Rupatali bus stop, on his way to the campus on Thursday.
"Naim paid Tk 3 as fare but the bus staff demanded Tk 5. After some argument, he was beaten up and thrown off the bus," said BU student Tahseen Azim.
Naim was admitted at the BMCH in critical condition.