From the Super Mario Wiki
The Pipeline Central is a field in Super Mario Strikers and Mario Strikers Charged made in honor of Mario and Luigi. It takes place in the afternoon, in the Mushroom Kingdom. The capacity is 15,000. It is made out of concrete and is the Flower Cup's special field.
Like its name suggests, the field has many Warp Pipes in the background and is located several miles in the sky. It is said to be "the highest elevated field in the history of the sport" according to the North American instruction manual.