Without assuming any knowledge on source's codebook and its output signals, we formulate a Gaussian jamming problem in block fading channels as a two-player zero sum game. The outage probability is adopted as an objective function, over which transmitter aims at minimization and jammer aims at maximization by selecting their power control strategies. Optimal power control strategies for each player are obtained under both short-term and long-term power constraints. For the latter case, we first prove the non-existence of a Nash equilibrium, and then provide a complete solution for both maxmin and minimax problems. Numerical results demonstrate a sharp difference between the outage probabilities of the minimax and maxmin solutions.