5 in the box, saints in 4-wide, though I think one of those guys is a TE. They leave backside guys unblocked, gives them 4 on three. In this case, AO has the weak A-Gap and Strong-B gap. MLBers sometimes have to gaps, based on the flow of the play. In this case it's a balanced formation, so in terms of numbers there is no strong side. Next read would be the wide side of field, in this case ball is in middle of the field. So, the last read would the tbe QBs throwing hand, which is the right. Also, Donald is on the left which tells me that;s the weak side. Same with Longacre...and Barwin is on the strong side.
So, the Saints run to the bubble, in this case the Strong-B gap. And they outnumber the Rams and the pursuit also fails, kmaking what could have been a 5-8 yard gain into a long TD.
AO go doubled, Brockers was grabbed and then there were Rams running into each other. Bad play.