XSp.

Apparently, some UFO sightings can be explained by a phenomena called Ball Lighting, which is a very rare form of lightning.

Dunno how many of the examples in the video are actually ball lightning sightings, but basically, it’s a lightning (the ones you see in storms) that get’s trapped in balls that can range in size, and can have some weird behaviour.
Dr. Paul Koloc is getting funded by government agencies to try to reproduce the phenomena in laboratory… but didn’t got much so far.
Which is understandable since the natural phenomena is already rare, and hard to reproduce even if it was common…

Source and more info: Gizmodo