Between George Floyd’s killing in police custody in May and Sept. 5, motorists drove into demonstrators at least 104 times, according to research by University of Chicago graduate student Ari Weil. There have been two reported deaths from such incidents.

Several have occurred since Sept. 5, when Mr. Weil stopped collecting his data, according to Roudabeh Kishi, the research director of the Armed Conflict Location & Event Data Project, a global crisis-mapping initiative. Dr. Kishi’s group counted eight such cases in the week of Sept. 20, and three the first week in October.

Many are accidental and appear to have happened when motorists were confused, according to Mr. Weil. In some cases, drivers have said they were acting in self-defense after having their car damaged by protesters and fearing for their personal safety.

Authorities have also charged 39 drivers with crimes ranging from reckless driving to vehicular homicide.