 The Celtics defeated the Dallas Mavericks in the NBA Finals last month to capture the franchise's 18th championship. Boston basketball partners purchased the Celtics for $360 million in 2002. One of the NBA's original and storied brands, the Celtics were valued at $4.7 billion last year by Forbes, placing them behind only the Golden State Warriors at $7.7 billion, New York Knicks at $6.6 billion,