I always grew up wondering what exactly caused lightning, thunderstorms and rains. High school physics later explained and taught me the reasons, facts and theories behind this exciting part of many wonders that nature has created. In fact it so happens that there is an Indian legend which explains the fact that every thunder and lightning caused is in fact a chariot move of the great Pandava warrior Arjuna who is refered to as Falguna when it comes to sky.
Coming to the aspect of Ball lightning, scientific data is of limited availability to explain fully about this interesting phenomenon. Its occurrence being irregular and of considerably less frequency to have data in place is a great challenge for the scientific fraternity to come to fully conclusive study. Though a lot of information and data available so far has been greatly derived from public reporting of the occurrence, there has been some studies that have produced meaningful insights into this.
Scientists have long attempted to produce ball lightning in laboratory experiments. While some experiments have produced effects that are visually similar to reports of natural ball lightning, it has not yet been determined whether there is any relation. Nikola Tesla was reportedly able to produce artificially 1.5" (3.8 cm) balls and conducted some demonstrations of his ability, but he was really interested in higher voltages and powers, and remote transmission of power, so the balls he made were just a curiosity. In summary, Ball lightning is a natural phenomenon, or debatably, a pseudoscientific theory. It is sometimes associated with thunderstorms. It takes the form of a long-lived, glowing, floating object, as opposed to the short-lived arcing between two points commonly associated with lightning.
A popular hypothesis is that ball lightning is a highly ionized plasma contained by self-generated magnetic fields, a plasmoid. This hypothesis is not initially credible. If the gas is highly ionized, and if it is near thermodynamic equilibrium, then it must be very hot. Since it must be in pressure equilibrium with the surrounding air, it will be much lighter and hence float up rapidly. Magnetic fields, if present, might provide the plasmoid's coherence, but will not reduce this buoyancy. In addition a hot plasma cannot persist for long, because of recombination and heat conduction.
There are a few more set of theories and hypothesis surrounding this interesting phenomena that surely makes it an interesting area. But it might take more research to exactly pinpoint the reason behind the ball lightning phenomenon. I definitely would like to experience ball lightning to know more and see what ball lightning looks like.