Many chemical reactions involve nonadiabatic transitions, for example, proton transfer reactions in solution. That is, while the reaction proceeds, it is possible that the electronic or vibrational state can switch between different adiabatic surfaces. Describing such processes is challenging, but essential to a correct prediction of reactions important in catalysis, biology, and many other applications. A number of methods have been proposed to treat reactions with nonadiabatic transitions, each with its own advantages and disadvantages. We present an adaptation of the classical mapping approach which treats electronic and nuclear degrees-of-freedom on an equal footing. Specifically, we extend the rare events approach to calculating reaction rate constants to include nonadiabatic transitions using this classical mapping approach. Some simple examples of barrier crossings with nonadiabatic transitions are presented.