The blockers job is to dissect which defender is the most dangerous man to make the tackle first and block him.
Drills which utilize the Vision-Decision-Action cycle are valuable in preparing players to move beyond the diagram and learn how to succeed in the chaotic environment that a football play presents. While at Notre Dame college, the #4 team in NCAA Division II in 2018, I saw a drill that had many components I liked.
The drill started with two players on offense and two on defense on the backs as illustrated in the diagram below. I should note that I am not a fan of the one-on-one tackling drill with players starting on their backs. There are much better and safer ways to teach tackling as outlined in our Shoulder Tackle and Advanced Tackling Systems. I would note that starting on players on their backs is not necessary to create the elements of a VDA drill. I would suggest starting players turned facing away from each other as a better alternative, especially at younger ages.