The phrase "a bold challenge" is correct and usable in written English.
You can use it to describe a task or situation that is daring or requires courage to undertake.
Example: "The team accepted a bold challenge to innovate in a highly competitive market."
Alternatives: "a daring challenge" or "a courageous challenge."
In picking Ryan, Romney was assigning himself a bold challenge.
This is a brave choice and a bold challenge to China's government.
The Forward prize called it "a bold challenge to historic definitions of poetic form".
Such a bold challenge to belief systems and predispositions induces uneasy contemplation.
In the Christian tradition, though, this view encountered a bold challenge during the Enlightenment.
"If you want to innovate, take a bold challenge, make a public announcement, and it will happen," Sinha said.
The spring meetings of the International Monetary Fund and World Bank take place this year against the backdrop of a potentially bold challenge to the world financial order: a BRICS bank to address the needs of the fast-growing emerging economies.
Practical complexity illustrates how critical complexification cannot be judged unambiguously: the fact that practice of critical complexification is difficult can be seen positively as a necessary and bold challenge and negatively as an insurmountable obstacle or even a threat.
It was a big, brash, and bold challenge to the icon pitcher.
The importance of the Drakes (they are mostly males, after all) is in their bold challenge to a corrupt system run by their bosses, the college presidents.
Finally, it came to them: a bold seasonal challenge -- a Christmas "Survivor" -- in which a family would be selected for a "living holiday window" display in Times Square.
