This article presents an account of syntactic ergativity based on the grammaticalization of a processing-based preference for nested as compared with crossing dependencies. We propose that ergative subject extraction restrictions arise because such movement would cross the prior Ā-movement path of the absolutive object and create an illicit crossed dependency. Our account predicts that arguments merged between the A-movement tails of the absolutive DP cannot extract, whereas arguments merged above or below them can. In developing an approach to syntactic ergativity grounded in sentence processing, we highlight the need for deeper conversation among formal, typological, and processing-driven syntax.