The board consists of 61 circles arranged in a hexagon, five on a side. Each player has 14 marbles which rest in the circles, and are initially arrayed as shown at left.
The player with the black marbles moves first. For each move, a player moves a line of one, two, or three marbles one space, either inline (parallel to the line of marbles) or broadside (not parallel to the line of marbles), as illustrated at left.
When one player has numerical superiority in a line (three to two, three to one, or two to one), he may push the opposing marbles with an inline move. Broadside pushes are not allowed. The winner is the first player to push six opposing marbles off the edges of the board. The diagrams at left illustrate three Black pushes, before and after pushing.
The diagram at left illustrates three situations in which it is impossible for Black to push. In the top line, Black does not have numerical superiority. In the middle line, Black has four marbles to three, but a maximum of three marbles may be moved each turn, so again no push is possible. In the bottom line, Black cannot push because it is forbidden to dislodge one’s own marbles.
I O O O O O
H O O O O O O
G + + O O O + +
F + + + + + + + +
E + + + + + + + + +
D + + + + + + + + 9
C + + @ @ @ + + 8
B @ @ @ @ @ @ 7
A @ @ @ @ @ 6
1 2 3 4 5
A popular notation: An inline move can be denoted by the movement of the trailing marble. Broadside moves can be denoted by the initial positions of the two extremities of the row followed by the final position of the first one (thus, with this notation, each broadside move has two notations possible, which could be avoided).
Here are some moves from a sample midgame. No marbles have yet been ejected in the first position.
The dynamics of the basic game may have one serious flaw: it seems a good, conservative player can set up his or her marbles in a defensive wedge, and ward off all attacks indefinitely. An attacker may try to outflank this wedge, or lure it into traps, but such advances are often more dangerous to the attacker than the defender. Thus, from the starting position, it takes little skill and no imagination to avoid losing, and nothing in the rules prevents games from being interminable.
Because it is boring for games to be drawn out indefinitely, serious Abalone players tacitly agree to play aggressively. A player who forms a defensive wedge and makes no attempt to attack is therefore likely to be a novice who might lose anyway. Nevertheless, the possibility of any competent player bringing the game to a standstill, and successfully avoiding losing to even a championship-calibre player, remains troubling.
There are several possible solutions to this conundrum. First, in tournaments, a judge may penalize a player for playing defensively. This solution is somewhat unsatisfactory, given that a judge may not always be present, and that "defensive play" is a subjective notion.
Second, several variations of the rules of play have been developed for the same board and marbles. None of the variations has the same appealing simplicity of the original.
The third, and perhaps best, alternative starting positions have been designed to make the formation of stalemate wedges less likely. Experiments are still underway to find an opening position, which neither devolves into a draw nor gives too great an advantage to the first player.One popular attempt are the Marguerite (daisy) positions, two versions of which are displayed on the left and on the right.
A number of two player variations use a third colour for passive pieces, for example variation The Pillar (with a fixed marble in the centre of the board), which has been examined to some depth by Alex Borello and Nicolas Le Gal. A few variations use a second layer of marbles.
Gert Schnider and Thomas Fenner participated to the evaluation and adjustment of Aba-Pro. Marc Tastet was the 1992 World Othello Champion, Stephane Nicolet is a two-time World Othello Championship finalist, and Jan Stastna is a strong Othello player.