[FrankWakefield]

It refers to a postseason game.

The Giants and the Highlanders played a 7 game series the second and third weeks of October, 1910. The Giants won that, 4 games to 2, one game resulted in a tie, called after 10 innings due to darkness.

In game 1 of the series on October 13, 1910, the Giants beat the Highlanders 5 to 1, Mathewson going the distance, scattering 8 hits, and striking out 14, a significant total in that time. He did not walk anyone, the one run the Highlanders got was unearned. The Giants got 5 runs on 12 hits and 2 walks, but only one of the runs was earned. Russ Ford went the distance for the Highlanders. It was a 1-1 tie until the 8th inning, when the Giants scored 4 in the bottom of the 8th. Mathewson lead off with a single to right, eventually scoring the winning run from third when Ford hit Al Bridwell with two outs and the bases loaded.

I think Scooter is right about the Yankee nickname being out there, but it not having been officially adopted yet.

Lots of cities would have these post season games back then, especially the cities with two teams.