A racing start in which the contestants are already in full motion when they cross the starting line.
A quick or auspicious beginning.
The start of a race in which the contestants are already moving as they pass the starting line.
Any rapid beginning.
(idiomatic) An especially good start.
The new restaurant got off to a flying start, packing out every night.
The start of a sports event in which the competitors are moving when they pass the starting line or initial jump point.
Origin of flying-start
From sailboat races, where the ships should be 'flying' under full sail as they cross the starting line.