They commit too many fowls.
Explanation: This joke relies on a pun involving the word “fowls,” which sounds like “fouls,” a term used in basketball to describe illegal actions that break the rules. The humor comes from the play on words; birds are classified as “fowls,” and the joke suggests that they wouldn’t be allowed to play basketball because they would constantly commit fouls. This clever wordplay connects the literal meaning with the sports terminology, creating a lighthearted twist.