Egypt's Interior Ministry said on Sunday that a fight between someone and one of the protesters led to Saturday's attack on the demonstration by the presidential palace.
Four men have been arrested as defendants while investigations continue, ministry spokesman said on Sunday.
In a Facebook statement, the ministry said that investigations have so far revealed that a scuffle between one of the now-arrested defendants and a protester started the attack that led to more than 15 injuries on Saturday.
The defendant had apparently come back with his neighbors and acquaintances following the confrontation with the protester and threw petrol bombs and fired birdshots at the protesters, burning four of their tents.
Some members of the central security forces were also injured during their attempt to contain the violence.