If you put a rb and a te in the slot with two wr, you have 21 with 4 wide. A common formation to try to get mismatches. The Browns run a 21 personnel with 5 wide on the Duke Johnson TD pass on Sunday. Both RB's lined up outside. Great designed play. Two LB's were covering both RBs. Think personnel, not formations. Before Hernandez went to jail, the Patriots used to run 12 with 4 wide (2 WR with Gronk and Hernandez). The could run hurry up, and pack it back in and pound the ball with the same personnel package. If you tried to substitute, they would spread em back out. Personnel chart for reference. I've recommended this book before, but I'll do it again. It really helps you take labels off of an offense and realize what a team is trying to accomplish. While I'm recommending stuff, Bernie Kosar has a show called 'Sports Zone', I love it. I wish he spent more time breaking down plays because he is a football genius, but it's awesome for those who appreciate his personality like I do too.