17 across
Boring
9
(4)
Boring 9 (4)
hints
0
checks
0
hints
The whole clue is the definition (& lit or double definition).
How the clue works
The first definition is Boring, meaning dull or flat. The second definition is 9, a cross-reference to 9 across (RACE), since a FLAT RACE is a type of horse race, so FLAT fits before that answer.