Leapfrog is an old game in which players vault over each other’s stooped backs. The first participant rests their hands-on knees and bends over, which is called giving a back. The next player places hands on the first’s back and leaps over by straddling legs wide apart on each side. The number of participants is not fixed. Games of this sort have been called by this name since at least the late sixteenth century.
Take a look at these interesting vintage photos of people playing leapfrog from between 1920s and 1950s.