While I am very pro on drones being available for doing cool stuff with this is an example of what can happen particularly with consumer level use of them. If you are using one you have to recognize the risk to other people either by inattention, misuse, weather (wind) and so on. They are exactly like flying an aircraft in the sense that you can’t get distracted, you have to keep your eyes outside (look out for others) and be prepared for an emergency landing or diversion at any time. It is very tempting with a small battery powered device that can operate in 3 dimensions to think that you can get close to observe a person or activity. The closer you get the less time that you will have to react to something unexpected (movement or wind for example). You have to recognize that you are the pilot and you are responsible for whatever happens. This is a good read to think about preparedness.

http://www.suasnews.com/2014/04/28431/unfortunate-event-as-triathlete-sustains-head-injuries-from-drone/