1a) The actual ground where Harold met his end?
1d) Where actors prepare to enter in secret (6,3,6)
4d) Wrestling contest loosens part of roof, say (9)
6d) Twice measure students in e.g. oboe, like Rimsky-Korsakov (6-9)
16d) Grass is infernal but not identical (9)
Apology for no lettes. All help much appreciated