It is usually written by a screenwriter who hopes to have the script optioned and eventually purchased by a producer, production company, or studio.
[2] Spec scripts are often written by unknown screenwriters looking to prove their storytelling ability and make a name for themselves in the film industry.
[...] Studios, distributors wanted the assurance of someone else having thought a property worth publishing [...] In those days, if you went to a party in the Hollywood community and somebody would ask, "What are you working on, Ernie?"
[3]In the late 1960s, William Goldman sold his spec script Butch Cassidy and the Sundance Kid to 20th Century Fox for US$400,000 in a studio bidding war.
[2] This could be a "development deal" – where a studio or producer asks a screenwriter to write another original script or adapt an idea or book into a screenplay.
[4] Outside of the traditional route of finding an agent, there are a number of competitions that a screenwriter can enter, such as the Nicholl Fellowship or Final Draft's Big Break Contest, among others.