First, I am not a lawyer. Yes you have a right to curse in public (see one example cohen v california), and cursing in itself is not obscenity (see miler v california). Cussing can be restricted in the captive audience such as you'll see in fcc v pacifica foundation, and to some extent within a school if it disrupts the classroom see ?fraizer? v bethal school district, and perhaps to phone calls as it makes a noise in the home (kovacs v cooper), as well as private property. So are you sure this is a public park, or is it a private park that is open to the public? If it is a private park, you have to comply with the owners wishes. There are exceptions to private property rules such as a case when a town gave a public park to a private owner so the park could prohibit blacks from attending, which the courts instead still recognized as a public park under I suppose a joint nexus. But special technicalities aside, if it is a private park your first amendment rights end. It is possible that the state created the park with limited fora, i.e. kids only, and each circuit may have their own rules-but the 5th and 11th circuit has rejected this for a family oriented community center when a group wanted to perform "hair" but not all circuits are the same. typically public streets and parks are traditional public fora, so there is no compelling governmental interest to restrict protected speech nor does what is called a sandbox effect take place as alluded earlier. see I think reno v aclu which cites I think sable v FCC. Furthermore, a prohibition of cursing words may violate the ADA in regards to people with certain types of tourettes syndrome. However, where some type of legal action is threatened, you'll NEED to seek a 1983 actions with injuncti and declaratory relief BEFORE violating the no cussing rule. You might be able to find a Federal civil rights lawyers who may take an easy case on the prospect of prevailing party attorney fees, but your group will have to stop playing ball until the attorney obtains an injunction because you'll lose your federal case the moment it becomes a state matter. (see Duram v salem inn inc). Furthermore, don't be surprised if they don't come back saying there are other public parks you can play ball in and curse-if they do that then they have effectively argued a time manner or place restriction while leaving you an alternative channel of communication. Even a time manner or place restriction would not be justified in prohibiting a person from cussing with verbal speech in public, nor would a t/m/p restriction be narrowly tailored-that is the government would be restricting more speech is necessary to achieve whatever their so-called interest is. Furthermore, I am sure that if you look all over the park you'll see grafitti and scratch marks of cuss words everywhere and the governments so called interest would be moot.