Champions Series (senior men's tennis tour)  Since 2006, the Champions Series is a series of tennis tournaments designed for former champion members of the ATP Tour. The Champions Series consists of tournaments played in select markets where top players of the sport compete in one-night, four-player events with two one-set semifinal matches and a one-set championship match played in one evening. Eligible players competing on the Champions Series have either held a Top 5 singles ranking; been a Grand-Slam singles finalist, or a singles player on a championship Davis Cup team during their ATP tour playing careers. The Champions Series allows one wild card of their choice at each event. The series is produced by Inside Out Sports & Entertainment. The minimum age to participate in a tournament is 30. In October, 2011, PowerShares QQQ signed a multi-year agreement with the Champions Series to become the title sponsor of this national tennis league of erstwhile ATP professionals. A new match format was introduced to complete all play on a single evening, with only four players involved. The new format is two semi-final matches consisting of a best-of-one-tiebreak set, followed by a one-set final for the championship. Prior to PowerShares QQQ, Outback Steakhouse served as the title sponsor of this seniors' league (as before Outback, the series was known simply as Champions Series Tennis). No matches were played in 2013 as the series realigned from the fall to the spring. Players are ranked based upon performance in each event and a cumulative total is kept each calendar year. Top ranked players of the past include:     The Oliver Group Champions Cup, March 12–16, 2008 The Residences at the Ritz-Carlton, Grand Cayman Legends Championship, April 16–20, 2008 Champions Cup Boston, April 30- May 4, 2008   The Oliver Group Champions Cup, March 7–11, 2007 Champions Cup Boston, May 2–6, 2007 Champions Cup Athens, May 17–20, 2007 The Gibson Guitar Champions Cup, August 22–26, 2007 The Championships at the Palisades, September 26–30, 2007 The Stanford Championships, October 18–21, 2007 The Legends Rock Dubai, November 20–24, 2007  Champions Cup Naples, March 10–13, 2006 Champions Cup Boston, April 27–30, 2006 The Championships at the Palisades, September 20–24, 2006 Stanford Championships, October 4–8, 2006 Stanford Cup, November 8–12, 2006