I tried something like this when I was a kid and about burned the house down. Took a thin sheet metal tube and capped it at both ends, drilled a small exhaust hole in one end, and then filled it with match heads. Then secured the tube to a long piece of hi-test line with two fishing line quick-detach swivel clips. The idea was to make a little rocket that could skate along the line. Didn't count on the fact that a whole bunch of matchheads in a confined space makes an incredibly hot flame. The tube basically melted as it scooted along the line, and the whole blazing chunk fell onto the grass near the house and caught it on fire.
My sister and I put it out with the garden hose, but had some 'splaining to do.
I don't know about a tennis ball, as it doesn't seem to me to be particularly lethal (Hit the dirt! He's got a fused Penn Championship!) but I have no doubt that the same number of match heads inserted into a capped piece of pipe and fused could easily kill someone.
Norm