This document presents a strategic model for determining when an MLB manager should challenge a call. It considers the upside potential of overturning the call based on win expectancy, the downside risk of losing the challenge for the rest of the game if not overturned, and the probability of the call actually being overturned based on historical data. Running the numbers in a scenario where the Mets manager is deciding whether to challenge a call, the model finds that the upside outweighs the downside and recommends challenging the call aggressively since the opportunity cost of losing the challenge is very low.