What is the fine-grained topic of the following text: Callis said recently on WEEI’s Minor Details podcast that he thinks Bradley might actually end up being a better player than Ellsbury, who just inked a seven-year, $153 million contract with New York, largely because of Bradley’s defensive prowess and power potential. Only return the topic.
Callis's comparison between Bradley and Ellsbury as players, focusing on Bradley's potential.