should we take 2d or 3d reality into consideration? )
Besides, it is not specified whether the elephants should be Indian (smaller) or African (bigger)
however, if we take Indian ones whose average body length is 6 meters and width 2 meters, and suppose thet they will be standing, and that there will be only one layer of them (2d space), and the field would be of average recommended size 105 \ 68 meters, the rough calculations will be as follows:
6x2=12 m2
105x68= 7140 m2
7140/12 = 595 Indian elephants!
of couse, if they were lying, dead or tied up, and could be packed in layers, we could calculate their volume and the way to pack them into a stadium, but if the stadium is not roofed, their amount would be limited only by gravity and density of their bodies...