Jordin Sparks -- Flips the Bird to Seahawks Fan

It was the battle of the birds ... Cardinals vs. Seahawks ... and Jordin Sparks let hers fly right in the direction of a Seattle fan this weekend -- and TMZ Sports has the pic.

Sparks -- a die-hard AZ Cards fan -- was singing the National Anthem at University of Phoenix Stadium in Glendale this weekend ... when a fan in a Seahawks beanie got her attention.

We're guessing there was some smack talk between the two sides ... and it culminated in a pretty solid one-finger salute from the former "American Idol" champ.