At approximately 3:18pm, Boston Police Officers responded to a radio call for a person with a gun at Hosmer Street and Blue Hill Avenue in Mattapan. Upon arrival, officers observed a group of males walking down Hosmer Street towards Blue Hill Avenue. Witnessing an exchange between two individuals within the group, officers stopped the group. One individual continued to walk down Hosmer Street while the rest of the group stopped on the sidewalk. When ordered to stop by police, the individual began to run down Hosmer Street. Officers then observed the suspect remove a silver colored firearm from his waist area. The suspect ran into a driveway on Hosmer Street with the firearm in hand. Officers ordered the suspect to drop the gun and suspect responded by pointing the gun at officers while continuing to run behind a house. The suspect was then seen throwing the weapon before jumping over a chain-linked fence. Officers recovered a loaded .357 magnum firearm and apprehended the suspect in a vacant lot on Hosmer Street. Njisane Chambers, 18, of Milton will be charged with Assault & Battery with a Dangerous Weapon, Unlawful Possession of a Firearm, Unlawful Possession of Ammunition, and Trespassing. He will be arraigned tomorrow in Dorchester District Court.