The players choose numbers to move a ball on a court.
Draw a court by dividing a piece of paper into four columns. Blue takes the left-hand half of the court, and Red the right-hand half. The ball starts in the centre.
The players start with 50 points each. At each move both players write down how many of their points to spend on the next move. The player who wrote the highest number moves the ball towards the other player. Both players then subtract their number from their remaining points.
Play continues in this way until either the ball is knocked out of the court, or neither player has any points left.
As in tennis, the player who has the ball on their side at the end of the game loses.
Here's an example. For the first move Blue chooses 5 and Red chooses 10, so Red has the largest number and moves the ball one step towards Blue. They are then left with 45 and 40 points respectively.
Play proceeds as follows:
After five more moves neither player has any points left, and the ball is on Red's side, so Red loses.
Here's another example. This time Blue tries to win by choosing large numbers, but runs out of points. Red can then keep choosing 1 and win the game by knocking the ball out of the court:
This is one of a family of bidding games in which the players each have a fixed amount of money to spend, and they bid to win each round.
This nice variant was originally described in Mala, Matthias. Das grosse Buch der Block- und Bleistift-Spiele. Fränkisch-Crumbach: Tosa-Verlag, 1995.
A version with three steps on each side was marketed with a plastic board and counters as Quo Vadis by Invicta Games in 1978.