If you're interesting in the long, under-celebrated history of American soccer, I can't recommend enough the uploads from Youtube user "soccermavn." There are old ads, footage of NASL's glory days, and even video of the short-lived United Soccer Association. (Update: He apparently got lots of these tapes from Dave Wasser's massive collection.) And yesterday, he uploaded something special: 33 seconds of the 1924 U.S. Open Cup Final.
It's the Fall River (Mass.) Marksmen vs. Vesper Buick (Mo.), and best we can tell, it's the oldest extant film of professional soccer in America. (This footage, reportedly of Irish sides Glentoran and Cliftonville from 1897, is the oldest overall.)
Soccermavn adds a little detail about the match, the footage, and a possible provenance:
Fall River Marksmen, champions of the American Soccer League, travelled to St. Louis to face Vesper Buick, champions of the St. Louis Soccer League. Before a crowd of 14,000 at High School Field, the Marksmen completed their "double" with a 4-2 win. The match was tied 1:1 at the half, but Fall River prevailed on a brace by Fred Morley and goals from Johnny Reid and Harold Brittan. Harris (whose goal is captured on film) and McCarthy scored for the St. Louis team. Findlay Kerr notched the win in goal for Fall River; Labarge manned the pipes for the losers.
As near as I can tell, this footage is excised from a Movietone or Pathe newsreel from the era. Alas, the raw footage of the complete match is probably long gone.
While the music abruptly ends, the fact is this is all of the footage.
My research has suggested that Thomas Cahill—former USSF Secretary—independently filmed many St. Louis league matches.
A Youtube commenter brings up an important point: Soccer lore holds that Arsenal and Chelsea were the first teams to wear numbers on their kits, starting in the 1928 season, but Vesper Buick were apparently doing it at least four years earlier.