On the roof of Campbell Hall in the southwest corner lies a 4-square court. If the computers go down, or it's late on a friday afternoon, or you really just need to blow off some steam, grab a ball (in 753 Campbell), grab some people (in 753 Cambell, inter alia), and play.

The basic rule is simple: if the ball strikes your square, then you have to hit it into someone else's square before it hits the ground, or else you're out. The walls don't count: treat them like reflections that don't change anything about whether you're out or not — and people waiting their turn to play count as walls.

4-square is a game of 4 players, and others waiting to play. The square nearest the telescope is the “King” or 1st square. The square immediately to its south is 2nd square, and the square immediately to its west is the 4th square. The third square is in the corner. Each square is held by a single player. During play, the players may roam outside their squares, though this may make it difficult to defend their squares.

Upon being put out, a player leaves the playing area and the other players advance, each moving to the next lower-numbered square vacated by the other players. Thus, if the player holding 2nd square gets out, the 3rd player takes the 2rd square, the 4th player takes the 3rd, and a new player takes the 4th. New players always enter at the 4th square. Players waiting to play may gather around the sides of the playing area and participate as “walls” (though they need not be completely passive). These players need not form a physical queue for the 4th square, but should take turns with the most recently put out player waiting for the others to play before rejoining the game.

The walls of the courtyard, the telescope dome wall, the stairs, doors, windows, and any other permanent fixture on the roof is considered a “wall”. Except during service, walls have no effect on the rules of the game. A ball bounced against a wall then into the ground is treated as though it had been sent directly into the ground. A player who bounces the ball off of a wall into his/her own square is out (“own square”) because a player who strikes a ball into his/her own square is out — the fact that the ball struck the wall does not change the ruling.

Players waiting to play typically stand outside and along the playing area. They should not stand in the squares nor should they block the path of players moving outside the squares. After a fair serve, they are treated for rules purposes as walls. They may strike the ball (which may adversely or beneficially effect players expecting the ball to continue past) or dodge it as they please. In this way, revenge may be extracted on the players who got them out.

Walls should NOT interfere with the serve, reach (far) into the playing area, or catch the ball.

Play continues until someone is out. The moment someone is out the ball is dead and no one else can be out until the next service.

You are out if:

1. the ball strikes your square and the next thing it touches (other than a wall) is the ground.
2. the ball strikes YOU and the next thing it touches (other than a wall) is:
   • the ground out of bounds (“Out”),
   • your square (“Own square”), or
   • you (“Double hit”)
3. you fault on a serve (“Bad serve”)
4. you are struck by the serve when you hold the 4th or 2nd square.
5. you catch the ball (“Carry”)

The player holding the 1st (King) square serves to the player holding the 3rd square. The server may not stand on or touch any part of any square until the ball is struck. The player must drop the ball, allow it to bounce once in the 1st square, and then strike the ball UNDERHAND. Once the ball is struck, service has begun and play continues until a player is out. No one can be put out until after the ball is struck.

The server is out (on a “bad serve”) if

1. the ball does not immediately hit the third square or another player.
2. the ball immediately strikes the wall (This is an exception to the usual rule that the walls do not change the status of the ball. For the purposes of this rule, observers waiting to play are not considered “walls”)

To prevent interference on the serve from the other players, any player other than the one holding the 3rd square struck by the serve is out. This rule is badly abused, so other players should watch out.

Residents of 751B hate 4-square and have been known to end a game by stealing the ball. Don't even ask them to close their doors or windows in the heat of July and August. It's been said they can tolerate 4-square for tasty treats or money.

Interference on the part of people waiting to play is grounds for a re-serve. The player holding the 3rd square must remain in the 3rd square until the ball is struck.

A server who faults due to the server standing in a square during the serve is technically out, but this is rarely enforced for minor infractions or for inexperienced players.

The game is refereed by consensus and good faith. If you know you are out, you should say so to stop play and leave the playing area. When a play ends and it is not clear to all involved who should be out, the player who “walks” is out. That is, if a player begins to leave the playing area is dismay, (s)he is presumed out for some infraction, even if it's not clear which one. If the outcome of a play is unclear, then the most plausible reconstruction of events put forth generally should be accepted.

The lines delineating the squares are governed by the strips of metal between the slabs that make up the playing surface. It can be unclear which side of a line the ball has landed on. In these cases, consensus rules, except when the metal strips are struck by the ball. Whenever the metal is heard to “clang”, the ball is presumed to have landed inside the square marked by the metal strip, appearances to the contrary notwithstanding. For instance, if the metal strip lies in the 2nd square, then hearing the ball strike the strip means that the ball struck the 2nd square, even if it otherwise apparently hit the 3rd square. This can be particularly important during serves and when a ball very nearly lands in the 2nd or 4th squares (a fault).

DO NOT KICK THE BALL OR HIT IT UPWARDS: the ball might go over the edge of the building.

First time players generally get a few “free” faults on serve until they get the hang of it.

If no consensus can be formed on who is out, the ball is re-served.

Creative forms of service and defence of service are encouraged.