More than 100 protestors were injured when Islamists backing President Mursi fought with opponents of the Muslim Brotherhood who have taken control of the government and are preparing to write a new constitution.
A government is in place, but Islamists and liberals are at loggerheads over the drafting of the new constitution, which must be agreed before a new parliament can be elected.
Many of the thousands who gathered in Tahrir Square were angry at this week's court ruling that acquitted former officials charged with ordering a camel and horseback charge on protesters in the uprising that ousted Hosni Mubarak last year.
But even before that ruling, Mursi's opponents had called for protests against what they say is his failure to deliver on his promises for his first 100 days in office.
"Down, down with rule by the guide," Mursi's opponents chanted, suggesting that Muslim Brotherhood leader Mohamed Badie pulls the strings even though Mursi officially quit the Brotherhood on taking office.
"Mursi, Mursi," the president's backers responded.
Some demonstrators pulled down a temporary podium that had been erected on one side of the square for speeches. Later, Islamists took over the square, triggering scuffles in nearby streets as they tried to keep rival groups out.
"We went to protest against the constituent assembly and Mursi's failure in his 100 days, and Islamists prevented us and are now controlling the square," said Islam Wagdy, 19.
There was no intervention by police, who have often been the target of protesters' anger in the past because of their brutality against demonstrators in last year's revolt.
The question for the Islamists relating to the new constitution is how much sharia and how fast. For the secularists, it is no sharia, but Islam will form the basis of all laws passed.
Mursi and his Salifi allies in the Nour party will seek to pack the constitutional committee with their like minded friends and freeze out more secular oriented reformists. You can probably expect more of these street clashes as the committee moves forward.