On first ave on the other side of safeco next to the tracks there are plenty of places and lots of tailgaters ,pop up tents,beer pong and sack toss tables , even people who bring tents,big screens and tarp off areas where they set up their chairs to watch pregame and the other games in progress
I think thats what you're after
Don't quote me on first ave but it is easy to find if you go to the east side of safeco, it starts under the off ramp from the freeway that goes to their parking lot and goes about 6 or 7 blocks
There are a lot of others but this is easy to find
ENJOY