tl;dr: Under the right conditions the step leader of a lightning strike can have a small bunch of electrons out in front of the rest of the tip, and the extreme

tl;dr: Under the right conditions the step leader of a lightning strike can have a small bunch of electrons out in front of the rest of the tip, and the extremely strong electrostatic forces at play can then accelerate that bunch ahead of the tip to relativistic velocities. The bunch then hits the ground and releases an intensely strong (hundreds of gigawatts) coherent microwave radiation pulse. Also under the right conditions this microwave pulse can get trapped as a standing wave inside of a plasma bubble which it maintains through its own energy, lasting for several seconds. Scientists should be able to test this theory and create ball lightning artificially if they can build microwave devices in the 100 GW range.