to be at the scene (sitting for an exam, performing, competing, giving directions etc)
firsthand (experience)
impromptu (remarks etc)
Definitions (粵典–words.hk)
副詞
喺正式場合依照當時嘅形勢作出改動或者應對 on the spot
辯論比賽好睇臨場表現嘅。
辩论比赛好睇临场表现嘅。
bin6 leon6 bei2 coi3 hou2 tai2 lam4 coeng4 biu2 jin6 ge3. The performance on the spot largely counts in a debating competition.
Definitions (Wiktionary)
verb
to be at the scene (such as in an exam, contest, game); to be on the spot; to be in the actual situation