Molecular dynamics simulations are used to explore the atomic-scale chemistry and associated wear that occurs when diamond surfaces are placed in sliding contact. The simulations predict complex radical chemistry initiated by the shearing of hydrogen atoms from chemisorbed molecules. Observed chemical mechanisms include hydrogen abstraction from the surfaces, radical recombination, transient surface adhesion, and formation of debris at the interface. These simulations provide the first glimpse into the rich, nonequilibrium tribochemistry that occurs at diamond and related covalently-bonded interfaces.