Back-Court Hairline

Alright listen up, chucklenuts! This joke is saying that a man's receding hairline is so far back on his head that it's like a "back-court violation" in basketball. You see, in basketball, the backcourt is the half of the court farthest from the offensive team's basket, and a back-court violation happens when the offensive team takes the ball over the half-court line, and then dribbles or passes the ball back behind the line. Basically, the joke is saying the man's hairline has retreated so far back, it's crossed the line. That's gotta sting, you genius.