Well alot of people that don't know the stadium, will buy pavilion seats as they know they'll at least have a seat. Then they pitch up and see hey, look we can sit right next to the cheer-leader girls and even get some signatures from the players standing right in front of me....and then they end up on the grass. The pavilion is a little "removed" from the action at times.
The grass isn't that bad, just bring your own chairs and it's better than the pavilion by far. Of course the grass runs the risk of being overly crowded and you might not get a "clean" view [i.e. someone higher than you in front of you] , where on the pavilion people are assured of their space....