21 down
9
boot
(4)
9 boot (4)
hints
0
checks
0
hints
The whole clue is the definition (& lit or double definition).
How the clue works
The 9 refers to the answer at 9 across (RACE), and a SACK RACE is a well-known event, so SACK fits before it; separately, to boot someone out is to SACK them. Both halves point to SACK, giving a double definition.