What does "Racing world" mean?

The [American] [car] racing world. Articles are often omitted from headlines. The "world" of racing is the totality of all the people and organisations who are involved with racing.

Other examples

The football world
The scientific world
The medical world

The Racing World would include everybody involved in racing: the drivers, the mechanic crews, the broadcasters, the fans and more. So it means:

Everybody who loves or is involved with racing is really excited and interested about Danica's first Sprint Cup competition.

(Not exactly an exciting or punchy headline.)

Joe(varoom, va-room)Nation

Excellent!
Thank you both.