Sam Smith says that it's a coincidence that his song "Stay With Me" is similar to Tom Petty's "Stand My Ground" but won't hang his hat on independent creation, where one author creates an identical or similar work without access to the previous work. Perhaps Mr. Smith is concerned that he may have subconsciously infringed Mr. Petty's work since he so quickly offered a writer's credit and royalties to Mr. Petty. With pop music, access to the original work is presumed because no one can avoid hearing pop music in the doctor's office and shops. If the two works are strikingly similar to the ears of an ordinary listener, it's copyright infringement. So you be the judge and let us know what you think.
George Harrison 'stood his ground' and 'wouldn't back down' when Bright Tunes sued him for copyright infringement of Ronnie Mack's "He's So Fine" (made popular by the Chiffons in 1963) with Harrison's "My Sweet Lord." The court found him liable of subconscious copyright infringement.