CNN has the full story:

Tokyo, Japan (CNN) — Four American teenagers, all children of U.S. military personnel, have been arrested on charges of attempted murder after a woman was knocked off her motorbike with rope strung across two poles, Japanese police said.
The four suspects — two 15-year-old boys, a 17-year-old girl and an 18-year-old man — were taken into custody on Saturday, the Tokyo Metropolitan Police Department said.
They are accused of causing a severe head injury to a 23-year-old restaurant employee by stringing a rope between poles across a road.