Former NBA star Derek Fisher has joined " Dancing With the Stars" season 25. Derek, 43, most recently served as the head coach of the New York Knicks until he was fired in February 2016 for the team's underwhelming performance. Prior to that, he played in the NBA for 18 seasons, most famously with the Los Angeles Lakers, with whom he won five championships. Shark Tank shark Barbara Corcoran, former Paralympic swimmer Victoria Arlen, and actor Frankie Muniz are set to join the cast for the upcoming season when it premieres on Monday, Sept. 18.