Why did the pumpkin lose the boxing match?

The joke “Why did the pumpkin lose the boxing match? It let his gourd down” is a play on words combining the sport of boxing with a pun on the word “gourd.” In boxing, the phrase “let your guard down” means to lower one’s defensive stance, making oneself vulnerable to punches from the opponent. The humor arises from substituting “guard” with “gourd,” which is a type of fruit similar to a pumpkin. Since a pumpkin is a kind of gourd, the joke whimsically imagines the pumpkin as a boxer who lost because it lowered its “gourd” (a play on guard).