The ballpark model is a system under which users of a facility do so at their own risk. The name arises from the fact that visitors to a ballpark bear the risk of getting hit by bats, balls and other objects flying into the stands at high velocities. An example of this type of system is New Hampshire's lack of a requirement that motorists carry liability insurance. The risk of getting hit by a driver who has neither insurance nor the means to pay for damages is borne by other motorists.
It is in contrast to the Disneyland model.
References
Ballpark model Wikipedia(Text) CC BY-SA