The incident took place about 3:30 p.m. in the 12000 block of Greywing Square.
The suspect assaulted the victim, took property and fled, police said. The victim incurred non-life-threatening injuries.
Officers then located the suspect and arrested him. Police charged Jaime Villatoro, 21, of Reston, with robbery and drunk in public.
In other crime news from Reston District Station:
2000 block of Cobblestone Lane, property from vehicle.
11400 block of Washington Plaza, property from business.
2300 block of Hunter Woods Plaza, merchandise from business.