A 28-year-old Fall River man dropped a bag containing a gun and more than 50 grams of cocaine as he was being chased by police in South Boston, State Police said. A K-9 unit trooper stopped the man, who was driving a motorized scooter, just after 10 p.m. Sunday on William Day Boulevard for a motor vehicle violation. The man fled on foot, State Police said in a statement. Once the suspect was apprehended, police recovered the bag. Inside were a Ruger .45-caliber handgun with obliterated serial numbers and 56 grams of cocaine, the statement said. The suspect also had a large amount of cash on him, which police believed was from selling drugs, the statement said.