Adams sold the rights to the novel to film-maker Martin Rosen in 1976. Rosen was originally planning to act as producer and overseer of the animated project whilst John Hubley directed, but Hubley quit after arguments with Rosen, who took over as director. The film was released in 1978 and proved a critical and commercial success. Rosen went on to direct an animated version of another Adams novel, The Plague Dogs, in 1982. Rosen retained control of the film and television rights to Watership Down, acting as a producer or licence-holder on both an animated TV series in 1999-2001 and the recent CG-animated 2018 Netflix mini-series.
The Richard Adams Estate, working under the title Watership Down Enterprises, raised a concern that Rosen had not paid the correct royalties to the estate on profits made by the film and TV series and their related merchandising lines following Richard Adams' death in 2016. Rosen also profited from an audiobook of the novel, despite audio rights not being part of his original deal.
The Intellectual Property Enterprise Court (IPEC) ordered Rosen to pay costs to the Estate and also an initial payment of $95,000 for infringing copyright, agreeing unauthorised deals and denying royalty payments. His control of the Watership Down TV and film rights was also summarily terminated with immediate effect and control reverted to the Estate.