Wikipedia-Sega v. Accolade said:
The court determined that the fourth factor, effect on the market, also weighed in Accolade’s favor. A court may not find fair use if an infringing work would take the place of the original work in the market. But the court notes that the Copyright Act was not intended to create monopolies, it was intended to foster creativity. Thus, the court finds that Accolade’s largely original work is merely an acceptable market competitor of Sega’s work. While natural market competition might have a negative financial effect on Sega, the court found that the benefit to consumers compelled a finding that the fourth factor weighed in Accolade’s favor. Therefore, the court found that Accolade had engaged in fair use.
[edit]Trademark
The Sega code in question, which Accolade incorporated into their games, caused the Genesis system to display the message "Produced by or under license from Sega enterprises ltd". Sega argued that Accolade had infringed their trademark by releasing games that displayed this message without Sega's authorization. Accolade, in turn, argued that Sega was at fault for displaying this message and falsely claiming credit for Accolade's games.
The 9th Circuit held for Accolade. Accolade prominently labeled their games as "not authorized by Sega", and the Sega message was only displayed to get the games to run, rather than to mislead. In contrast, Sega deliberately was trying to limit competition in the video games market -- an impermissable grounds for falsely claiming credit for games produced by legitimate competitors.