Acting with fierce, lion-like energy; working or fighting with frenzied force and determination (yojijukugo).
彼は試験勉強で獅子奮迅の努力を見せた。
He showed frenzied effort while studying for the exam.
チームは獅子奮迅の活躍で逆転勝ちを収めた。
The team made a comeback thanks to ferocious play.
社長は獅子奮迅の決断で会社を立て直した。
The president rebuilt the company through decisive, fierce action.