When Dad ends up in the hospital, Josh angrily tells Mom that he's upset "because our backboard is splintered." In doing so, he draws a direct connection between the backboard on a basketball hoop--which keeps missed shots from going out of bounds and can be used to bounce the ball off of to make baskets--and to Dad, who performs a similar function in the Bell family. Like a backboard, Dad keeps Josh and JB in line and constantly points them in the direction of success.
The The Crossover quotes below all refer to the symbol of The Backboard. For each quote, you can also see the other characters and themes related to it (each theme is indicated by its own dot and icon, like this one: Note: all page numbers and citation info for the quotes below refer to the Houghton Mifflin edition of The Crossover published in 2014.).
The timeline below shows where the symbol The Backboard appears in The Crossover. The colored dots and icons indicate which themes are associated with that appearance.