Someone needs to teach MW how to tackle

Well that's kind of the point. He didn't have to cut back, he believed in his own speed and/or thought Williams didn't have the angle. If Williams plays it hard, I've got no doubt he cuts back but because he was the only defender there I think you have to try to make that play. Better to try and fail than fail because you didn't try.
Anything is better than just letting him score. You have to attempt a tackle not an escort. Football 101