The web site say the lawn chair has to be 9 inches from the ground, do they check this and can you bring the standard chair that you would take to a kids ball game?

The Tommy Bahama type are often seen there. They have straps to carry on your back and a small bag for your stuff. They do not provide chairs except in the handicap area between the lawn and the regular seating. Those are regular chairs. They do not rent chairs, I asked the last time I was there.

Yes they do can only have chairs that are low to the ground like beach chairs

Yes but you can get a chair there for free just be a little early