Paul is implicitly speaking of Christ's servants as if they were athletes. (See: [[rc://en/ta/man/jit/figs-explicit]] and [[rc://en/ta/man/jit/figs-metaphor]])
This can be stated in active form. Alternate translation: "they will crown him as winner only if he competes by the rules" (See: [[rc://en/ta/man/jit/figs-activepassive]])