white knight

white knightは文字通り「白い騎士」という意味ですが，文脈によっては「政治改革者, 運動［主義］の闘士」あるいは「乗っ取り攻勢を受けた企業を救うため友好的な買収を申し出る会社」という意味で用いられます（『プログレッシブ英和中辞典』小学館）。ここでは「身売りされそうになったチームを救った救世主」と解釈できます。
ちなみに以前Othelloくんがwhite knight syndromeという表現を扱っていますので，そちらも合わせて押さえておきしょう。（Koyamamoto）
cf. http://d.hatena.ne.jp/A30/20120928/1348813229

Seattle tech community, NBA basketball go way back
Steve Ballmer's efforts to bring an NBA team to Seattle are getting a second act.
The Microsoft CEO, a well-known basketball junkie, let down local basketball fans in 2008 when he couldn't finalize a deal to buy the Seattle SuperSonics as the team was sold to out-of-towners with the intention of moving it.
Ballmer was viewed as a last-minute white knight to wrestle the team away from Oklahoma businessman Clayton Bennett and keep it in Seattle. After all, Ballmer is one of the richest people in the world; he was a regular courtside presence at Seattle's KeyArena, where the Sonics played; and, according to The New York Times, Ballmer helped coach his son's basketball team. Ballmer also played early-morning pickup games.
http://www.usatoday.com/story/tech/2013/01/21/seattle-nba-microsoft-steve-ballmer/1852643/