The suspect stopped the sedan in the middle of the intersection of Ocean and Colorado Avenues, near the Santa Monica Pier, shortly before 1 p.m. and exited with a leashed dog.
Los Angeles Police Department officers approached the suspect as he lay face-down on the pavement and took him into custody without incident.
The dog, apparently uninjured, jumped back into the Toyota Corolla and was later taken into custody by officers.
The LAPD did not immediately provide details about the alleged assault with a deadly weapon or what the suspect was believed to be armed with.