Source : Webster's Revised Unabridged Dictionary (1913)

Leapfrog \Leap"frog`\, n.
   A play among boys, in which one stoops down and another leaps
   over him by placing his hands on the shoulders of the former.

Source : WordNet®

leapfrog
     n 1: advancing as if in the game of leapfrog
     2: a game in which one child bends down and another leaps over
     v 1: jump across; "He leapfrogged his classmates"
     2: progress by large jumps instead of small increments
     [also: {leapfrogging}, {leapfrogged}]