Feedback-driven winds from star formation or active galactic nuclei might be a relevant channel for the abrupt quenching of star formation in massive galaxies. However, both observations and simulations support the idea that these processes are non-conflictingly co-evolving and self-regulating. Furthermore, evidence of disruptive events that are capable of fast quenching is rare, and constraints on their statistical prevalence are lacking. Here we present a massive starburst galaxy at redshift z=1.4, which is ejecting ~46% of its molecular gas mass at a startling rate of >10,000 solar masses per year. A broad component that is red-shifted from the galaxy emission is detected in four (low and high J) CO and [C I] transitions and in the ionized phase, which ensures a robust estimate of the expelled gas mass. The implied statistics suggest that similar events are potentially a major star-formation quenching channel. However, our observations provide compelling evidence that this is not a feedback-driven wind, but rather material from a merger that has been probably tidally ejected. This finding challenges some literature studies in which the role of feedback-driven winds might be overstated.