The two dinosaurs were trapped together and fossilized. They were a velociraptor and a protoceratops (more specifically a Velociraptor mongoliensis and a Protoceratops andrewsi.) A crew of Polish-Mongolian paleontologists found this scene in 1971. It was found in the Gobi Desert in Mongolia. So how were they frozen in battle together?
The actual answer for such a question is not certain, but it appears the dinos may have been drowned in sand from a sand dune collapse. They were definitely killed at the same time. The fossil shows how aggressive the velociraptor was, reaching out with its claws, a predator by nature.
The velociraptor’s nature is to attack the prey, grasping it with its “grasp[ing] its prey with its forelimbs, while kicking and raking the belly and chest with its hindlimbs.” In the fossil, the protoceratops is fighting against the velociraptor’s grasp for its life, while the velociraptor is aggressively holding onto what might have been its next dinner!