The next year, Epyx published World Karate Championship for home computers, which sold 1.5 million copies.

The district court found that Epyx had infringed on Data East's copyright, but not their trademark, and ordered an injunction against distributing World Karate Championship.

[14] One of the most influential cases in this area was Atari v. Amusement World from 1981, where the court listed numerous similarities between the games Asteroids and its alleged clone, Meteors.

[14] Despite twenty-two similarities, the court determined that these were unprotected ideas that are inherent to the game concept of shooting rocks in space.

[12] At the time, it was one of the only cases to rule in favor of the defendant, based on the idea-expression distinction that copyright does not protect broad ideas, only unique expression.

Since they provided no evidence that they created their game independently, the similarities were strong enough for the district court to infer that Epyx likely purchased it and discovered the underlying program.

[1] A major factor in the ruling was the determination that the average consumer, a 17.5 year old male, would subjectively regard the two games as substantially similar.

[17] Writing for the appeal court, Judge Stephen S. Trott noted that copyright disputes seldom have evidence of one party directly copying another.

[20] However, the court determined that these characteristics, "which consist of the game procedure, common karate moves, the idea of background scenes, a time element, a referee, computer graphics, and bonus points, result from either constraints inherent in the sport of karate or computer restraints.

[20] After excluding unprotectable elements, such as functional rules and generic scenes related to karate, the court determined that the remainder of the games were not substantially similar.

[22] The Data East v. Epyx case was also cited in Apple Computer, Inc. v. Microsoft Corporation, where the court said that unprotected expression could not support any finding of infringement.

[25] Even outside the software industry, Pasillas v. McDonald's Corporation cited the legal principles from Data East v. Epyx to explain that infringement cannot be proved through similarity between standard elements.

[26] This case is remembered for building on the legal reasoning in Atari v. Amusement World, where the courts first applied the scènes à faire principle to video games.

[27] At the time, the Santa Clara High Technology Law Journal observed that the decision would provide more clarity about what similarities are considered infringing, bringing video games into conformity with other audio-visual works.

[14] Contrasting it with later rulings, intellectual property attorney Jack Schecter noted it among early cases where "courts seemed to have a difficult time conceiving of copyright protection that would extend beyond the strict confines of the art and sound assets included in a game.

[12] Legal scholars have determined that the permissive approach to video game clones shifted in 2012, with the rulings in Tetris Holding, LLC v. Xio Interactive, Inc. and Spry Fox, LLC v. Lolapps, Inc.[12][22][28] Courts have noted the increased graphical power of modern video game platforms, which opens up new possibilities for artistic expression compared to early cases such as Data East v. Epyx, when it was harder to express an idea in new ways.