Plimsole

The plimsole line around a ship originated as a game. A rope would be tied to the mast, and a sailor would have to walk around the ship horizontally, keeping to the line.
After several mishaps with sailors trying to run too fast, chasing each other, or worse, practicing the game while at sea, the practice was outlawed, and a new use for the lines was found.

_{All content copyright Tom Crowley}