The chance of getting the ball doesn't come into it! How many times have you seen a player knock the ball quite a few yards ahead of an opponent (with another opponent having the opportunity to get to the ball first) only to be trimmed out by the guy he's trying to go past? Loads of times. And it's a yellow card every time. It is not dependent upon where the ball is when it is in play.
If I was the ref (and I've done a fair bit in my time) and you ran into an opponent, then I would give a foul against you.
And it doesn't matter what direction an individual is running in, if they are fouled, it's a foul.
And Werner was absolutely trimmed out by the Sheff Utd goalkeeper, who committed himself and just ploughed into him. Keeper probably thought Werner would knock the ball in the same direction as Werner was heading so dived at his feet, expecting to get the ball. Werner flicked the ball one side, and went to go past the goalkeeper on the other. Result: no ball for the GK to collect, and going at the speed he was, he took out Werner. Penalty.
What's not to understand...?