A regulation is in the works in Portola Valley that would establish criteria to determine when a professional such as a tennis instructor will need to obtain an agreement with the town to teach at public recreational facilities such as the tennis courts at Town Center.

In a nutshell, occasional one-on-one lessons arranged by residents will not need town scrutiny under the plan, but an agreement and insurance will likely be necessary for instructors whose sessions have the tendency to displace residents.

The Town Council, at its March 23 meeting, agreed to consider three factors governing the need for a permit: frequency of use, intensity of use, and the number of students who are from out of town. Staff is working on ordinance language.

No residents have complained, said Assistant Town Manager Janet McDougall. But because the town does have a formal relationship with a tennis pro who has an agreement and has paid for insurance, an instructor on a nearby court without such an agreement would have an unfair advantage, Ms. McDougall said.

"Parity and liability are the issues," she said.

The council split initially on whether to craft a regulation that covers all scenarios. Councilman Steve Toben, an attorney, imagined an example of an aerobics class on the central lawn at Town Center in which students are asked to jump on to and off the low wall there. One of them might fall and the town could be liable.

Should the regulation be broad enough to cover that, Mr. Toben asked. The town could ease up on the restrictions over time if they proved onerous.

The suggested alternative has the ordinance aiming at the tennis courts and all-sport/basketball court at Town Center, and broadening it later if necessary.

Since the soccer and baseball fields are already well regulated, Councilwoman Ann Wengert suggested that the ordinance, for now, be directed at the Town Center courts.