The “reproducibility crisis” has been one of the most significant stories in science in the past 15 years and has led to significant policy changes across the research landscape. Yet, scandals, irreproducible studies, and cries of crisis have occurred for decades in science. This article seeks to explain why the reproducibility crisis has taken root and become a force in science policy in ways previous crises have not. In short, we argue that it was through the scientific, institutional, and cultural efforts of a group of scientific activists we are calling metascientists. Metascience is a scientific social movement that seeks to use quantification and experimentation to diagnose problems in research practice and improve efficiency. It draws together data scientists, experimental and statistical methodologists, and open science activists into a project with both intellectual and policy dimensions. Metascientists have been remarkably successful at winning grants, motivating news coverage, and changing policies at science agencies, journals, and universities. The social movement lens is useful for understanding the popularization and impact of the reproducibility crisis narrative and suggests ways the institutions of science are adapting to meet a changing political and technological landscape.