Noun
duck on a rock
(sometimes hyphenated) A traditional children's game in which multiple players stand behind a throwing line and each takes a turn throwing a stone (sometimes called a "duck") at a target rock (sometimes called the "drake") that is guarded by another player, such that when a player's thrown stone dislodges the target rock all the players run to retrieve their thrown stones, while the guard replaces the target and then attempts to tag a player before he or she can return to the throwing line. If the guard successfully tags a player, then the guard and player swap roles.
Naismith's handwritten diaries, discovered by his granddaughter in early 2006, indicate that he was nervous about the new game he had invented, which incorporated rules from a children's game called " Duck on a Rock ", as many had failed before it. Source: Internet