Police arrested an 11-year-old girl Monday after she allegedly threw a rock at a 12-year-old girl at a Kalihi middle school earlier in the day.The younger girl approached the older girl while she talked with friends and allegedly threw a rock at her forehead for no apparent reason at 10:13 a.m.

The 12-year-old was taken to the hospital with a cut and contusion to the forehead.

Police found the girl at her home at 12:50 p.m. And arrested her on suspicion of second-degree assault.