He let his gourd down.
Explanation: This joke plays on the pun between “gourd,” which is a type of squash, and the phrase “guard down,” commonly used in boxing to refer to a fighter being unprotected. The punchline, “he let his gourd down,” humorously suggests that the pumpkin’s downfall in the boxing match was due to being careless. The humor comes from the clever wordplay, creating a lighthearted connection between pumpkins and boxing.