Just an awful hit here. Bernard Pollard of the Ravens caught Patriots running back Stevan Ridley right in the helmet.
Ridley went unconscious, fumbled, and Baltimore recovered. They scored a few plays later to make it 28-13.
It wasn't an illegal hit because Ridley actually lowered his head into Pollard's path, and Pollard kept his chin up and didn't launch himself helmet-first. But it's hard to watch.
Here's the GIF via @cjzero: