Ex-Seahawks Star Walter Jones -- Buy My Mansion ... Get a Football Field

Seattle Seahawks legend Walter Jones just SLASHED the asking price for his Alabama mansion ... and it's the perfect spot for a serious fan looking to play more than just fantasy football.

The 9-time Pro Bowler bought the 8 bed, 9 bath, 13,450 square foot pad back in 2005 ... and first tried selling the place for $3.5 million back in 2011 -- but now he's knocked half a mil of the price.

The house is an athlete's dream palace -- there's a full football field (with NFL sized FG posts) ... a basketball court, tennis court, swimming pool, workout room ... and a detached "sports house."

Non-sports nuts will have to settle for a home movie theater, game room, spa-bath ... and an ELEVATOR.

Jones is considered a shoe-in when the new Hall of Fame inductees are announced tomorrow ... so the 'bama spread could be a legit piece of NFL history.