The Cleveland Police Department said that two officers were assaulted and received minor injuries during the protests. It is unclear what protesters were demonstrating about. The 18 arrests brings the total number of arrests at the RNC to 23, according to police.
Riot police and mounted cops were deployed, and some areas were placed into lock down. The majority of protesting around the convention has occurred in Public Square, a central plaza close to the arena where the Republican gathering is being held. Images on social media showed groups of police dressed in black riot gear, marching through a portion of the street.
A line of police cordoned off a section of the street, keeping protesters to one side.
Tensions between police and protesters began to rise after they tried to burn an American flag. Police officers rushed in to put out the flames. Protesters were given an order to disperse, and some refused.
Photos of the protest showed a man dressed in black, wearing a black cap, waving the burning flag in the air.
Earlier today, protesters gathered around a call to "Wall Off Trump," and many people carried signs bearing that expression.
Yesterday entrances to Public Square were closed off briefly to separate two different groups of protesters and keep them from fighting, according to police.