Nine members of Jefferson City high school’s volleyball team suffered moderate injuries when their team bus rolled backward Monday afternoon at the school.

Jefferson City Police say the bus was parked near the high school’s front door and that the driver exited the bus and went inside the building as students began boarding. JCPD investigators say that for unknown reasons, the bus started to roll backward downhill, ran off the road and struck a sign, pole, parked vehicle, concrete retaining wall and a dumpster.

JCPD officers say seven of the nine injured were taken to hospitals for treatment.

Our news partner ABC-17 reports the bus was about to transport the volleyball team to a match in southwest Missouri’s Lebanon when the bus rolled backward down Union street.