"Radical action" refers to taking extreme or significant measures to bring about change or solve a problem. It involves taking bold and decisive steps that may be different from conventional or gradual approaches. Full definition
We like it when a company recognizes that its stock is deeply undervalued and takes radical action to capitalize on it. (greenbackd.com)
You need radical action of the type we have been taking in the past 18 months to set us on a new course. (politics.co.uk)
In 1968, three landmark productions — an exhibition, a publication, and a magazine project — set off a decade's worth of radical action in Japanese contemporary art and photography. (brooklynrail.org)