Many nouns can be both countable and uncountable. In the first instance, 'defeat' is countable, a single instance of the condition; in the second instance, 'defeat' is an uncountable condition generally considered.
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snvplayerWhy is there "a" before the defeat in the first sentence, but no "a" before the defeat in the second sentence?It's worth noting that "crushing" describes what kind of defeat is risked. Adjectives like "crushing" modify nouns. We might say that "defeat" here is a 'pure noun'. It means 'an occasion of defeat'.