Wait — “partially retractable roof”? Who would conceive of not having something temperature-controlled there?
gonna guess they aren't so much concerned about rain as they are about shade for fans? they probably can grow natural grass due to the high sun angle and why give a rat's pattootti attitude towards water conservation (most likely gray water to irrigate so they get a LEED certification

). At night, it can get cool and it will be open. i imagine very few day games other than April and late September.