The stadium conditions are not good. Also acceptable imo
Why is there no 의 after 경기장?
It is not necessary (i.e. it's implied that 상태 is about 경기장 without 의)
"The stadium is not in a good condition" should be accepted;;
競技場 狀態가 좋지 않습니다.
The Olympic stadium is not a good condition should be accepted!