Well Nike have called their fencing shoe the "Ballestra", but as far as I can tell, all the reputable fencing websites spell it with the single "l". Indeed, one fencing forum discussing the Nike shoe correct the spelling and refer to it as the "Balestra".
But the clincher seems to reside in my Italian dictionary, where a "balestra" is defined as a crossbow, which really is an extremely apt way of thinking about this particular move.
Finally, though, in the process of pursuing spelling, I found this little video demonstrating a bal(l)estra. The commentary is kind of annoying (simplistic) and the demonstration not very inspiring, but it more or less conveys the idea.