What rules of the ancient Roman game 'Harpastum' are known?

All this is based on HARPASTUM, from AerobiologicalEngineering.com: (Original source citations are from my own research)

Harpastum was known as the Small Ball Game. The ball was "small" by virtue of its not being as large as a follis, paganica, or soccer-sized ball. This was a hard ball probably about the size and solidity of a softball.

This game was apparently a Romanized version of a Greek game called phaininda. It involved considerable speed, agility, and physical exertion. It must have been played on dirt or a lawn, not on a court, since players often ended up on the ground. In Greece, a spectator once had his leg broken when he got caught in the middle of play.

We know little about the exact rules of the game, but it appears to bear a remarkable resemblance to American Football and Rugby. Harpastum was a team game that probably had a variable number of players. It was played on a demarked rectangular field, probably about the size used in field hockey.

Atheneaus - Athenaeus: The Deipnosophists, Book 1, 26: (Original Greek is found here...)

Harpastum, which used to be called Phaininda, is the game I like most of all. Great are the exertion and fatigue attendant upon contests of ball-playing, and violent twisting and turning of the neck. Hence Antiphanes, "Damn it, what a pain in the neck I've got." He describes the game thus: "He seized the ball and passed it to a team-mate while dodging another and laughing. He pushed it out of the way of another. Another fellow player he raised to his feet. All the while the crowd resounded with shouts of Out of bounds, Too far, Right beside him, Over his head, On the ground, Up in the air, Too short, Pass it back in the scrum."

Galen, in On Exercise with the Small Ball¹, describes harpastum as:

...better then wrestling or running because it exercises every part of the body, takes up little time, and costs nothing. He also considered it profitable training in strategy, and said that it could be played with varying degrees of strenuousness...

Translation by Alexander Adam of a passage from Isidor:

Ludere expulsim, vel pilam geminare volantem -- When they snatched the ball from one another, and threw it aloft, without letting it fall to the ground.

The general impression from these descriptions is of a game quite similar to rugby. Additional descriptions suggest a line was drawn in the dirt, and that the teams would endeavor to keep the ball behind their side of the line and prevent the opponents from reaching it. This seems rather like an 'inverted' form of football. If the opponents had the ball on their side of the line, the objective would seem to be to get in and "pass" it to another player, or somehow get it back over the line.

From these descriptions, the diagram at right (below) provides a typical starting position. Perhaps 5-12 players on each side of a line, on a field about the size of a football field. A team that won the toss of a coin (dice or tali have been mentioned in this context) would start with the ball sitting on their side of the line. The opposing team would try to steal the ball and get it back to their side. Presumably only the person holding the ball could be 'held,' which is why the player above passed it while dodging an opponent -- he was in danger of being tackled. Scoring might be accomplished by letting the ball hit the ground in your own territory (?), which may be why the ball was not allowed to hit the ground. The other characteristics of the game, such as players or balls going out of bounds, could be expected to be similar to modern rules of soccer or football.

_{¹ P.N.Singer, "Galen: Selected Works" (1997), pages 299-304}