Based upon standard chess rules... but...
All the "pieces" are fighters and wear the same color tunic or baldric with the name or image of their "piece" as well as a scarf, pennon, or handkerchief with the same color and marking -- this will be their token.
No live steel. In normal play distance weapons i.e. bows, are not allowed. All combat must comply with standard SCA combat rules. Bopper weapons can be used if not played as a combat tourney.
The opening Gambit. A single round of combat decides which side will choose to make the first move or give the other side the first move. The gambit match will also decide the opening position of each team i.e. which side of the board to choose since terrain inconsistencies may be present. The team leader chooses the Gambit piece from the pawns on his team.
If a pawn makes it to the other side of the "board" that pawn becomes their team leader's choice of a Rook, Knight, or Bishop even if those pieces have yet to be removed from the board. i.e. It would be possible to have more than two Rooks, Knights, or Bishops in play on a team. Pawns must be promoted to maintain an even ration of Knights, Rooks, and Bishops for "his" team. (Example: If there are currently 2 Rooks, 2 Knights, and only 1 Bishop on "his" team, the pawn will be promoted to Bishop.) No pawn can return as a King or Queen. A pawn may move two positions "his" first game movement.
When one chess piece attacks another piece it is NOT an automatic removal from the board. The battle is fought for the position on the board. Both pieces drop their tokens on the board position being contested. The two pieces combating for position may move out of their board position without penalty. The losing piece removes his/her token from the field and is removed from play. The surrounding pieces have the option to drop their token in their current position and may remove themselves from the area of the combat. The pieces not involved in a challenge for position have 45 seconds to leave the area of combat (if they so choose) and 45 seconds to return to their correct position upon the game Marshal announcement of the winner of the position challenge. Upon resolution they will return to their prior position. If a surrounding piece does not remove itself from the area of combat "he" must drop "his" token, that piece may intentionally or inadvertently interfere with the course of the combat for position. If a piece interferes with combat that piece may not cross the boundary of their position unless attacked by one of the combating pieces under penalty of removal from the board, additionally, either piece in combat for position has the option to attack any piece that intentionally or inadvertently physically interferes. Note: If not killed by one of the combating pieces an interfering piece once attacked may become a "Rogue".
A Rogue piece may move freely about the board and combat any one piece that has remained upon the board during the combat that caused the piece to become rogue. If a Rogue combats and loses "he" is removed from the game. A rogue is immune to any special benefits/restrictions normally placed upon "him" and "his" opponent. The Rogue takes the place of any piece he kills and is no longer "Rogue". A King "gone Rogue" is considered dead and succession takes place.
If during the course of movement a Knight moves through an occupied position "he" must request passage from the occupying piece. If passage is not granted, the Knight has the option to combat the occupying piece, challenge for passage, or gain passage though the occupied position by what means he may. If combat ensues the losing piece is removed from the board. The occupying piece may not leave the boundaries of "his" position unless engaged in combat. "He" must return to his position as above or leave the board dependent upon the outcome of the combat. If passage is granted the moving Knight must peacefully continue along his route.
If a Bishop combats any piece except another Bishop, the position combat is conducted as follows: If the Bishop wins the first round of combat "he" wins the position. If "he" looses the second combat for position he is removed from the board. In the event of combat between two Bishops, a single round decides the position winner.
When a Rook wins a position combat the opposing piece is "imprisoned" by the Rook. In subsequent combats, if the Rook moves into a combat and looses "he" releases "his" choice of "his" prisoners and returns to "his" prior position on the board. If another piece moves into position to attack a Rook and looses the Rook imprisons "him". If the attacking piece wins "he" has the option of returning to "his" prior position and releasing all the Rook's prisoners in which case the Rook remains on the board or "killing" the Rook and removing the Rook and all of the defeated Rook's prisoners from the game. A prisoner released returns to "his" game starting position. If that position is occupied, the released prisoner must combat to regain that position. If a Rook is defeated and holds no prisoners "he" is removed from the game. A Rook may not imprison a King or a Queen but may "capture" a Queen.
If a Queen looses a combat for position, she is not removed the board, instead she is captured. If the Queen is captured "she" may be ransomed back to the opposing team. * Any ransom cannot add or remove pieces from the playing field. No ransom will be allowed that provides mundane monetary or other benefit to an individual or a group that is not a charitable or non-profit organization. All ransoms must be "negotiated" by the bards of the teams in play. If the capturing team's bard does not offer a ransom for the Queen, the captured Queen's team bard has the right to challenge to win their Queen back. Challenges cannot be combat challenges. All ransoms or challenges must take place upon the field during the chess match. A Queen returns to the field in "her" beginning position, however, if that position is occupied "she" enters the field in "her" choice of the unoccupied positions of "her" teams beginning positions. A single Queen can only be ransomed or challenged for thrice during a match. The queen engages in combat as per a queen in standard chess.
The team leader has 2 minutes to announce his/her move. The team leader may consult with non-players or special advisors during the course of the game but not with the pieces. Pieces may yell out their preferences and other such tidbits of information or opinions they feel like sharing with the field but the team leader may not ask (or signal) for their opinion. Once an intended move is stated it may not be withdrawn and must be "played". The team leader must be a non-combatant.
Team leaders may make up to three substitutions of pieces during the match but only at the request of the piece(s) to be substituted. The substitutions may not have already been a piece on their team in the current match. A substitute piece may be a fighter previously not in the match or enlisted from captured, killed, or imprisoned pieces of the opposing team.
If one side only has a King left on the board that King may move in a straight horizontal, vertical or diagonal line anywhere on the board provided the move ends in combat. Otherwise, the King can only move one square at a time as per normal chess. When both sides only have a King on the board both Kings move to the center area of the field and combat for the win. A King may only declare a successor while in combat. The King's successor must be a piece in play and may not be the opposing team's King, Queen, or Gambit. The King's successor may not be changed once named unless "killed" prior to succession. If a King is killed without a successor the successor is automatically the Gambit and then the Queen of the King's team, though, if both the Gambit and the Queen have been removed from play prior to the death of the King, the successor is chosen from the opposing team and proclaimed by the deposed King's team herald (presumably, but not necessarily, by audience proclamation). If the successor is chosen by public proclamation "he" may not be the opposing team's King. Upon succession the successor has the option of moving to "his" team's beginning King's position or taking up the crown from "his" current position. If the successor's team's beginning King position is occupied, the new King must combat for the position or remain in the position "he" occupies when crowned. There is NO checkmate. All pieces must drop their tokens and remove themselves from the field during a King vs. King combat. All combats involving a King are decided from best of three rounds.
Taunts, jeers, shouted insults, and encouragement by the players and spectators are highly encouraged.