The tennis ball comes flying out of the cannon with a tremendous noise and speed. If this cannon is aimed at the far wall of the lecture hall (not towards students), it can almost bounce off of the wall behind the cannon after the ricochet. The tennis ball is capable of putting a dent in a wall that it strikes directly.
The spark from the Tesla coil causes the volatile system to react. The isooctane quickly reacts with oxygen to form a huge amount of carbon dioxide. This reaction is accompanied by a large increase in heat. Between the additional gas volume and the additional heat, the pressure becomes so high so quickly that the cannon goes off.
An NSF funded Project