Evan Davis, from the British reality show Dragons’ Den, defied BBC strikers. If you defy someone, you refuse to obey or to follow the wishes of someone. In this case, he defied his coworkers at the BBC who were on strike.
How did he defy the will of these strikers? He crossed the picket line. A picket line is literally a line or procession of people who are publicly protesting. The expression, to cross the picket line, means a worker continues to work while his coworkers are on strike.
When Davis crossed the picket line, he provoked a furious row. A row is a very noisy argument or serious disagreement between people. This noun is pronounced like “wow!”