First, I agree with those who have said it should be 'choke', rather than chock. However, if the original really said and meant to say chock, then I would take that to mean, "to stop a hippo". A chock is an object placed in front of, and often partially beneath, a wheel to prevent movement. This would be strange to my AE ear, but entirely understandable. There are so many crimes on his record that they could, if piled together, prevent a hippo from moving. That said, I still believe it should be choke.