square off

squareは「四角いもの」を思い浮かべると思いますが、動詞の用法もあります。「2乗する」や「…を四角に仕切る」(『ジーニアス英和辞典　第４版』大修館書店)はご存知かと思われます。
見出しのsquared offはLDOCEに"American English to get ready to fight someone"と定義されています。「戦う準備をする」といったところでしょう。天安門広場(Tiananmen Square)とも掛かっていると私はとらえました。(Minnesota)

Journalists and censors square off in China

In the past few days, Chinese journalists and their supporters have launched startlingly direct opposition to Communist Party rule, protesting a heavy-handed move by Guangdong's provincial propaganda department to unilaterally replace a Southern Weekly editorial on constitutionalism with pro-Party bromides. Defying censors' directives, media organizations around the country continue to post messages of support of Southern Weekly reporters who have gone on strike and called for the dismissal of provincial propaganda chief Tuo Zhen. It is the 21st century equivalent of carrying placards through Tiananmen Square.

http://www.cpj.org/blog/2013/01/in-china-online-rebellion-grows-over-southern-week.php