Think of it as just another kind of kite.
Primary hang glider instruction in Cesar Chavez Park has been shut down by the City, citing the Land Use Plan for the park:
"The publicly owned land north of Spinnaker Way should be used for unstructured public recreation. The area will be pedestrian and bike oriented (with no public roads through or around the area), protected from the intrusion of incompatible uses."
Whether hang gliding is an "incompatible use" is an open issue - the "intrusion" referred to in the plan was intended to keep out various forms of motorized recreational vehicles. This does not preclude unanticipated uses; it is worth noting that no form of kite flying was anticipated in the park plan.
Certainly the laissez-faire tolerance for unusual and diverse activities such as hang gliding is a valued characteristic of this park, and is very much within the spirit and intent of "unstructured" recreation.