What does Filthy learn about what it means to be “Da Man”?

"Da Man" is more of a hero-figure archetype personified by Dad. Dad's championship ring fascinates Josh and JB, who see it as a symbol of their father's legacy and power. Dad got the ring in recognition of his prowess on the court, and it should be an honor when Josh gets it at the end of the novel. However, at that point in the story, Josh is not that pleased to inherit it on his own, thinking about how being "Da Man" did not save his Dad in the end. Symbolically, then, he tells JB they are both "Da Man" and the ring belongs to both of them; thus, Dad is represented by both of his sons, who can learn from his mistakes and represent different aspects of his personality.