How do I solve 16 down in Daily Telegraph Cryptic 3370?

Question

Accepted Answer

16 down reads "Brilliant place to play baseball" (7 letters); the answer is DIAMOND. It's a double-definition clue: two separate definitions of the same word sit side by side. No wordplay split and no indicators — both halves of the clue define the answer. The full step-by-step breakdown is on this page.

Brilliant place to play baseball (7)

16D — Brilliant place to play baseball (7) — DIAMOND