Ultimately you as an individual would be responsible for the actions of throwing the disc, and it would be you vs. the plaintiff. Now in this instance that you posted, due to the continued repeats of concern (the notation about the several e-mails) a lawyer felt that the city was negligent in their process of protecting the interests of the public by ignoring or failure to alter the disc golf course after years of repeated requests. The 2006 city council comment isn't a good one either.
This is why Cliff Drive will be redone this year. There will be more activity, and when a park becomes more multi-use driven, it must adapt in all parameters. Now bear in mind we have a TON more green space to work with than CA does in most areas here, so our ability to alter a course to coincide with other partners is easier. I for one though have always worked on playing devils advocate for the WORST possible shot EVER and who would it impact. This is why communication and partnerships with all parties within the parks is part of the solution to working good/great courses. They must work hand in hand to build the best, to be the best, and be able to adapt to keep that line moving forward with all ideas and attractions.
The goal in Cliff is to have more activity than most parks have in the region, and changes are being made to make that happen. However when the land was first being walked in 2000 out there by a few of us, none of that entered the mind, because it was so neglected. Now we have built and enhanced the park and enticed others to see visions to make it even better. Instead of holding the course hostage to progress, the desire from this designer is to make the course even better and create a much better course to compliment the designs going on within the improvements around the course.