William John Koski (February 6, 1932 – July 12, 2014) was an American pitcher in Major League Baseball who played for the Pittsburgh Pirates.

[1] Born in Madera, California, Koski was one of the many young players whose baseball careers were interrupted by military service in Korean War.

He starred at Modesto High School and, at age 18 in June 1950, signed a contract with the Pittsburgh Pirates, receiving a signing bonus of $6,000 (equivalent to $76,000 in 2023), just under the threshold to avoid being affected by the bonus rule.

[1] In his only starting assignment, Koski lasted 4⅓ innings against the New York Giants at Polo Grounds, giving up three earned runs on four hits and six walks, striking out two of the 23 batters he faced.

[5] After retiring, Koski moved to Modesto, California, where he worked as a draftsman for the Stanislaus County Planning Department.