### Instruction:
Why is the sport commonly known as "Ultimate Frisbee" legally recognized only as "Ultimate"?

### Input:
Ultimate, originally known as ultimate frisbee, is a non-contact team sport played with a disc flung by hand. Ultimate was developed in 1968 by AJ Gator in Maplewood, New Jersey. Although ultimate resembles many traditional sports in its athletic requirements, it is unlike most sports due to its focus on self-officiating, even at the highest levels of competition. The term "frisbee" is a registered trademark of the Wham-O toy company, and thus the sport is not formally called "ultimate Frisbee", though this name is still in common casual use. Points are scored by passing the disc to a teammate in the opposing end zone. Other basic rules are that players must not take steps while holding the disc, and interceptions, incomplete passes, and passes out of bounds are turnovers. Rain, wind, or occasionally other adversities can make for a testing match with rapid turnovers, heightening the pressure of play.

### Response:
The key reason why the sport "Ultimate Frisbee" is legally known as "Ultimate" comes down to copyright issues. The sports company "Wham-O" trademarked one of their products as the "Ultimate Frisbee" which would require licensing fees for the sport to use this name or risk facing legal action.