Abstract: The dynamics of a spherical version of the batch minority game (MG) with random external information will be discussed. After an introduction to the generating functional analysis of MGs and a discussion of the currently available dynamical approximations for the MG's key observable, the market volatility and for price return autocorrelations, we present a spherical version of the batch MG. This model is designed to be exactly solvable, but we find that it still displays a non-trivial phase diagram. In contrast to standard MG versions, we can calculate the volatility exactly. Our study reveals similarities between the spherical and the conventional MG, but also intriguing differences.