Ugandan opposition leader Kizza Besigye was arrested along with dozens of his Forum for Democratic Change supporters in Kampala.
Police used pepper and water to disperse the opposition team which had gathered at Nelson Mandela Stadium-Namboole where they were anticipating rally.
But police blocked Besigye's vehicle, spraying it with water. The opposition leader fell from the sunroof of the vehicle before he was arrested.
Authorities accused Besigye, a former ally of President Yoweri Museveni, of defying them over the change of the venue for the rally.
“FDC informed us about the intended celebration and were wrote back to them advising that they should shift the venue but they ignored our directive. Besigye defied police orders and parked his vehicle in the middle of the road, blocking and inconveniencing other road users.
"The car was towed away and he was taken to Naggalama Police Station. At the moment no charges have been preferred against him but investigators are still gathering evidence,” Kampala Metropolitan police spokesperson Mr Patrick Onyango said.
Kyadondo East MP Robert Kyangulanyi alias Bobi Wine condemned the latest incident, accusing President Museveni of disrespecting other leaders.
The Ugandan leader is preparing for 2021 polls after getting rid of presidential age limit through an act of Parliament. He clinched power in 1986.
"I condemn in the strongest terms, this savage, cruel and brutal treatment of Dr. @kizzabesigye1 by the Uganda Police," said Mr Wine.
"It is totally unacceptable for political leaders to continue being treated in this manner by the Museveni regime. This impunity has to end. Totally unacceptable."