The DE to the blitz is long sticking to the A gap and the OLB and Corner are coming off the edge. Williams is calling a man free coverage to create an overload. The two inside linebackers have man responsibilities on the running backs. The inside linebackers execute a key rush or rush to cover technique on the backs. The technique is simple, at the snap rush the back. If the back attempts to release into a route cover him. If the back attempts to set up for a screen the key rusher should be behind the releasing offensive linemen making screens to the RB difficult. If the running back picks up the other rushers the key rusher can add to the rush creating an overload.
Here the Saints overload the right side that has 4 blockers by bringing what turns into 5 from a side. With the running backs picking up the blitzers the key rushing linebackers are unblocked.
Video of this blitz can be seen here.
If the backs had split instead the inside linebackers would have still been in the rush and an overload would still be created. Only this time the overload would be a 4 from a side blitz vs. 3 blockers.