Contrast training is a form of resistance training that pairs a heavy strength exercise with a lighter power exercise to take advantage of a phenomenon called post-activation potentiation.
Post-activation potentiation refers to the acute enhancement of muscular contractions due to the contractile history of the muscles and central nervous system. In simpler terms, the heavy loading of the strength exercise generates a high degree of central nervous system activation, which results in greater power output during the following power exercise. As a result, contrast training is a great workout for developing power and speed for football.
Check out the workout over at Stack.