there are several scenarios that Aruba describes as "standard" for stadium installs.
1) under seat. this is literally what it sounds like. putting the AP under spectator seats. in this case omnis with allow or no squint deployed every 100 seats or so. topology uses body loss to isolate APs
2) under seating section. if structure allows using a 60x60 ( e.g. D607) or 90x90 degree sector antenna (e.g. D805) are suggested. verification of penetration characteristics are necessary for each variation in structure.
3) top down. this is a common topology for indoor stadiums or convention spaces. antennas deployed with the largest downtilt possible. they should have narrow bandwidths and low sidelobes. ANT-2x2-5314 and ANT-2x2-2314 are excellent examples of how this has been done the "right" way.
there are other variations and topologies but these get treated on an ad hoc basis.
stadiums cannot be deployed blindly. for this reason Aruba partners are usually engaged to engineer the solution for maximum operation and professional services capability is available to support this. please inquire with your local Aruba sales team.