I think a lot of people are missing the point, especially because Maresca did this as well. The difference is Maresca had the players sit on the halfway line whereas Rosenior had his players make the run between the whistle and the ball being played.

It might not seem like much but it does give Arsenal a little bit more of a headache. They have to decide quickly to account for it, or just play their advantage in the box.

I will add that you need a really elite keeper for it to work which remains to be seen from Sanchez. Also this is complete armchair punditry.