railbird

[reyl-burd] /ˈreɪlˌbɜrd/
noun, Informal.
1.
a horse-racing fan who watches races or workouts from the railing along the track.
2.
any kibitzer or self-styled critic or expert.
Origin
1890-95, Americanism; rail1 + bird in sense “frequenter,” as in jailbird, yardbird
Slang definitions & phrases for railbird

railbird

noun

An ardent horse-racing devotee: another three-year old that set the railbirds agog (1890+)