Cassette distribution of the hit movies "Platoon" and "Hoosiers" has been blocked by a federal appeals court in San Francisco. By a 2-1 vote, the 9th U.S. Circuit Court of Appeals on Friday prohibited Home Box Office Inc. from distributing videocassette copies of either film for sale or rent and ordered HBO to try to retrieve all unsold copies from retailers. The order does not forbid the planned showing of the films on cable television by HBO. The suit was filed by Vestron Inc., which says it bought home video rights from the production company, Hemdale, for "Hoosiers" in 1985 and for "Platoon" in April, 1986, before either film was released. After the films became successful, Vestron says, Hemdale delayed or refused to give prints of the films to Vestron and sold them instead to HBO for a larger sum. Lawyers for HBO and Hemdale were not available for comment.