One of the basic problems in the field of mechanical properties of polymers is the observation of the sequence of deformation events and the changes in microstructure associated with them during deformation at relatively high rates. Typically, well characterized polymer-samples are subjected to mechanical impact, and then various microscopy techniques are used to determine the deformation events (i.e., crazing, shear banding, cavitation) post mortem. Real time small angle X-ray scattering (RTSAXS) techniques, however, make possible the direct observation of scattering from crazes and voids while the deformation is in process. In this paper we report RTSAXS measurements, performed using intense synchrotron X-ray radiation, from a high impact polystyrene (HIPS) and an acrylonitrile butadiene styrene (ABS) copolymer during tensile impact. At a deformation rate of 4.2 cm/sec, (100 in./min), the ABS was found to absorb over ten times the impact energy of a HIPS sample. RTSAXS studies indicated: (1) that the ABS has a larger average craze fibril diameter than the HIPS (12.2nm vs. 8.7nm), (2) that localized shear occurs before crazing in the ABS, and (3) that the ABS sample generated 3.8 times the craze volume compared to the HIPS. The increase in craze volume alone, however, does not account for the greater toughness of the ABS, indicating the importance of the contribution of localized shear deformation to impact behavior.