Watch as Coach explains LB Play in Cover 4. The Mike LB is keying the #3 receiver. If the #3 receiver moves laterally the Mike LB looks inside for a receiver coming inside on a shallow route. If nothing is coming inside the Mike LB must drop and is responsible for #3 receiver on a vertical route. The outside LBs are keying the #2 receiver. If the #2 receiver goes out or vertical it is the outside backer's responsibility. If #2 goes inside the outside back gets depth looking for #3 crossing on a shallow route.