What constitutes a cause of action "arising from" protected activity?

Courts have not precisely defined the boundaries of a cause of action "arising from" such protected activity. ( 425.16, subd. (b).) "[T]he statutory phrase 'cause of action . . . arising from' means simply that the defendant's act underlying the plaintiff's cause of action must itself have been an act in furtherance of the right of petition or free speech. [Citation.] In the anti-SLAPP context, the critical point is whether the plaintiff's cause of action itself was based on an act in furtherance of the defendant's right of petition or free speech." (City of Cotati v. Cashman (2002) 29 Cal.4th 69, 78.)