Repulsor balls were small and maneuverable antigravity spheres used as missiles.
Such balls could outrun a speeding vehicle at speeds of over 250 kph, making them some of the Galaxy's deadliest weapons. When at nearly one meter of their target, the repulsor balls would detonate.
These weapons were best known for being used as the arsenal of the Fromm Tower Droids which were owned by the crime syndicate Fromm Gang in 15 BBY.