William Porter "Spike" Shannon (February 7, 1875 – May 16, 1940) was a professional baseball player and umpire.

Shannon was an outfielder over parts of five seasons (1904–1908) with the St. Louis Cardinals, New York Giants and Pittsburgh Pirates.

His batting average fell over the course of the next two seasons, though he remained a threat to steal on the base paths.

However, he continued to slump and on September 30, 1908, he played his final game, going one for four against the St. Louis Cardinals, ironically, the very team he'd made his major league debut for a few seasons earlier.

Hoping to catch the eyes of scouts and make his way back to the big leagues, Shannon signed with the Kansas City Blues of the American Association.

Shannon still made another comeback at the age of 38 a couple years later, this time for the Virginia Ore Diggers of the Northern League.