Since the beginning of the COVID-19 outbreak in Spring 2020, universities around the world have quickly adopted online teaching as an emergency measure. Informed by activity theory, the present qualitative case study aims to better understand the nature of the rapid institutional transition and its impact on academics’ pedagogical experiences during this period. A multiple set of qualitative data was collected in a national university in South Korea that rapidly made the online transition, following government directives in February 2020. This article provides useful accounts of the changes that occurred in interconnected teaching activity systems at the university while adopting online teaching, highlighting the complex factors underpinning individual academics’ experiences. The sudden shift in institutional teaching activities and conditions created a range of contradictions that were experienced as dilemmas by academics, the main subject of the activity systems. The results demonstrate that two groups of university faculty, separately identified as novice online teachers and expert online teachers, faced different dilemmas and challenges. An essential lesson learned from this analysis is the need for a more holistic, realistic, and sensitive approach to emergency teaching scenarios that may enable educational institutions to better respond to such emergencies in the future.