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 wrote this:
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 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.
In an epigram, Martial makes reference to the dusty game of harpasta in reference to Atticus' preference for running as exercise: