William "Cannonball" Jackman (October 7, 1897 – September 9, 1972) was an American baseball pitcher in the Negro leagues.

He played from 1925 to 1942 with several teams,[1] including a spot on the otherwise all-white East Douglas team in Massachusetts's amateur Blackstone Valley League in 1929, a squad which also featured 18-year-old newcomer Hank Greenberg.

[2][3] At age 55, Jackman received votes listing him on the 1952 Pittsburgh Courier player-voted poll of the Negro leagues' best players ever.

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