Rad is a slang term, short for radical. This movie shows what radical sports is when applied to car driving on NES.
Curiously, the game Rad Racer was made by Square, which is probably best known for its Final Fantasy game series. Quite a different game, this here...
If you decide to play this game, we recommend the Power Glove. It's so bad.
Downloadable encodes have the author's commentary as soft subtitles.