We report the development of a model-based leaping/flipping quadruped robot. The planar model contains a planar rigid body and two compliant legs to investigate how forces are transmitted from the ground to the body through the foreleg and the hindleg and the resultant forces and moment on the body. The spring-loaded compliant leg with rolling contact was chosen for analysis, while the widely-used spring-loaded compliant leg with point contact was also developed for comparison purpose. The model's equations of motion (EOM) were derived for four modes: double stance, hindleg stance, foreleg stance, and flight. Moreover, the factors of initial pitch angle and relative actuation timing that affect whether the motion is a forward leap or a flip were investigated. The results indicate that different factors dominate different indices of the leaping/flipping motion-body pitch variation is mainly determined by the initial pitch angle; lift-off angle is determined by the delay of the foreleg; and stance time is affected by the delay of the hindleg. The same parameters were applied and evaluated in a robot that exhibited the leaping and flipping behaviors predicted by the model.