I see Witten near the goal line. He runs a route, and essentially blocks out like a basket baller. He gets open. He finds that spot and moves the defender with his route.
I am not an expert. But what he does isn't speed. It is his intention, read by the defender.
I think back to the Indiana Jones film Last Crusade, and the knight who guarded the Holy Chalice. When the man drank from the brilliant golden chalice, he ended up dying.
The knight said, "He chose poorly."
I think of that every time I see Witten move the defender the wrong way.