This study examined how conceptual knowledge concerning batting preparation develops with playing experience and how this knowledge influences decision making during a simulated game situation. Twelve experts, their coach, and 12 novices viewed a half-inning of a videotaped collegiate baseball game and assumed the role of the fourth batter. Propositional-type analysis of subjects' think-aloud protocols revealed experts' conceptual representation of batting preparation enabled them to search through a highly restricted problem space, which facilitated the development of sophisticated condition-action rules used to solve the problem. Experts' rules were more tactical, refined, and associated compared to novices' rules. Experts were different from novices in what attributes were considered important to solving the problem. Experts generated self-regulatory strategies to update, check, and modify their predictions of pitcher characteristics. This study provides initial evidence of the nature of adult expert sport performers' conceptual knowledge underlying decision making in sport situations.