Competitive Coevolution of Robots to Play Ultimate Frisbee

This paper describes the coevolution of neural controllers for robots in a simulated Ultimate Frisbee play. The goal of these experiments was to reproduce established strategies for both offensive and defensive players in Ultimate, as well as to possibly discover novel strategies that could be implemented by humans. In each experiment, an offensive robot and a defensive robot compete for optimal positioning to receive/intercept a frisbee pass. Two closely-related fitness functions were designed to reward each robot for positioning with respect to its opponent and a stationary robot representing the player with the disc. Defenders evolved against a pre-programmed cutter displayed behavior resembling good man-on-man defense, and in coevolution, cutters developed the ability to make deep cuts when the defender was focused on guarding the in-cuts. 1 Evolving Intelligent Players In recent years, artificial intelligence and developmental robotics have taken on many challenges. Some, such as problem-solving and simple categorization, have been met with outstanding results, while others, such as natural language processing and computer vision, have proven quite complex. In this paper, we present a new challenge. Can robots learn to play a sport which is young enough to still be evolving itself? And if they can, might they also be able to develop effective strategies that humans have not yet invented? The answer to the first question will be of great import to the world of computer science, and the answer to the second will be of great import to the world of Ultimate Frisbee. If our robots succeed, it will help demonstrate the ability of machines to participate in and understand a small part of human activity, and it may help Ultimate players to think critically about established strategies. 1.1 Ultimate Frisbee: The Game Ultimate Frisbee is a team sport played on a rectangular field with end zones at each end. The goal of the offensive team is to advance a circular disc from one end of the field to the other, and a point is scored when an offensive player catches the disc within the opposing end zone. The disc is advanced by being thrown from one player to a teammate. A player may not run while in possession of the disc and has 10 seconds to make a pass or a change of possession occurs. The goal of the defensive team is to force a turnover of possession, either by intercepting passes or by preventing the offense from completing the pass such that the disc touches the ground. Seven players from each team are on the field during play, and the defense typically matches up one-to-one on each offensive player or distributes to guard regions of the field. The offensive team is divided between two roles: handling the frisbee (2-3 players), and cutting to receive passes (4-5 players). Handlers are typically more-experienced players who have developed throwing skills and good field vision.