Fallback in stellar collapse

We review the physics behind supernova explosions produced in stellar collapse. Assuming the convective region in the collapse drives the explosion, we can derive a maximum energy to the supernova explosion as a function of time after collapse. For explosions that take more than 0.5 s, the explosion energy is weak. Such explosions will lead to a lot of material falling back onto the compact remnant after the launch of the explosion. We estimate the amount of fallback and speculate about the role this fallback plays in driving further explosions and in r-process production.