LONDON (AP) — Long after drones became a key tool for militaries and spy agencies, authorities now realize the threat they can pose to sports events.

It’s not multimillion-dollar military-grade drones prompting concerns, but remote controlled contraptions costing just a few hundred dollars that can be sent soaring over stadiums. And, as the chaos at a soccer game in Belgrade last week showed, a provocative flag or banner being carried by a low-cost device can be a catalyst for disorder.