[just another ref]

Originally Posted by Berkut

You would really call that a foul, seeing it at full speed?

Here it is at full speed. The contact is basically simultaneous with the block.

YouTube - Derrick Williams game-winning block against Memphis

Probably not, but if the foul had been called, it was justified. As to the "zero chance of going in" part, that is debatable, and, by rule, not relevant.