William Samuel Haddock (July 28, 1875 – October 13, 1953) was an American athletic leader who served as president of the United States Amateur Hockey Association from its creation in 1920 until its demise in 1930.

[3] In 1919, he conducted an investigation into the death of Fannie Sellins, who was shot and killed during a miner's strike in Natrona, Pennsylvania.

Haddock contended that the wound was "deliberately inflicted, after the official autopsy...to discredit those in authority and for the further purpose of furnishing anarchistic, dangers and revolutionary agitators and organizers propaganda".

[9] He ran for a full term in 1929 on the Democratic and Fair Play tickets, but lost to Republican Charles Chamberlain.

[11][12] Haddock served as vice chairman of the International Skating Union of America and was treasurer of the United States Olympic Fund.

[18] Haddock served as secretary of The Pittsburgh Press' soccer league and was treasurer of the United States Football Association.