Which part are you commenting on? Is it the use of the word "legitimate"?

Because suing someone for patent infringement is a "legitimate" course of action, i.e. it's a lawful thing to do. In fact (AFAIK IANAL etc etc) it's the only way to ascertain whether a patent is being infringed or not without working with the opposition directly and sharing trade secrets outside the context of a court room with proper protections, something I doubt anyone would be particularly happy about.

If it's the "don't really begrudge the approach" part. I don't know that any of us really have the knowledge from within the golfing industry to know what different companies think of the practice.