It's what the West Coast was built off of. Johnny Unitas, Lenny Moore's blind toss sweep, Alan Ameche's gut run with a slant pass running behind it.
The gut set up the slant if the defense sinks on the run. The pitch if they line up inside and jam the tight end's release. If they sink the run and the outside corner sits the pitch or the linebacker flow(either or both) the slant comes open.
Run it to the side your quarterback leads with. He can then run towards the pass for a better release and accuracy.
Walsh changed things with the NFL and went back to the Ohio Valley offense(West Coast). He leads the halfback to the flat off the snap, and the slant was usually a bigger WR to handle the impact of a shorter pass route. Those two reads forced the OLB to get outside and close the slant/cover the flat. It then opens the way for the FB lead runs. Bill Ring, Tom Rathman, Wendell Tyler, Roiger Craig were using the same run option once saved for Ameche when the presence of speed like Lenny Moore opened up the field of play to the outside. Defense got so fast that a blind pitch was a bit more risky than a forward pass.
Paul Brown got the sprint option with Walsh, combined it with the Colts classic gut-slant read. Walsh brought people across formations and rolled out the QB to match footwork and tempo. His passing set up the run when teams camped outside for those routes it opened up interior and off tackle runs.
The West Coast primary read and checkdown came from the Baltimore area football which Al Davis was part of. Shula got it there also. Paul Brown had integrated those looks into the Browns, then Bengals sets. There he combined that with Walsh's horizontal stretch offense that he developed with Gillman/Al Davis coaching to compliment their vertical tactics.
Brown had less overall talent in Cincy than his Jim brown dynasty days, still had a vertical reciever(Isaac Curtis) mobile QB and a good pass catch TE and backs. He had more specialized talent, and Walsh tailored what they did best into ball control looks that limited how deep the QB set to limit mistakes and possible turnovers. Field position play that still got points while controlling time.
The Baltimore area, a combination of Schools with a background of military acadamies competition, was where great football schemes draw their roots. The same places that trained soliders and generals helped develop coaches and talent evaluators that became big parts of today's game. Al Davis was a coach and scout for the region, and he scouted for Baltimore.
There it joined the work of other great minds and became what it is.
The East Coast offense merged with Gillman's vertical game which Davis was part of. Bill Walsh brought it to Brown's Ohio Valley offense. The first West Coast superbowl was coaches from within the Paul Brown coaching tree/organization(Walsh and Forrest Gregg, a Hall of Fame lineman for Lombardi).
The more passing heavy West Coast won over the run oriented East Coast style of the same scheme. Both teams set high standards for competitive play in the era. The Niners built a dyansty, proof of how fundamentally sound the West Coast offense was is evidenced by the Niner's victory in which they were almost outgained in yards two to one, and no runner on the team got near 100 yards. The Bengals threw for more in the game as well, proof the West Coast is about percentage and conversions, not stats. Stats just come with execution and defensive breakdowns, as Walsh added more talent his teams got more points.
Gregg was a straight shooter, a lot like Marv Lewis. The Bengals have returned a coach of character back to their team and are showing signs of success from having done so.
http://www.bengals.com/press/news.asp?news_id=1915
The google cache had a reference to Forrest Gregg, their current site didn't have anything to note his era there. More needs to be said, their approach is once again task-centric and will accomplish the goals needed to be winners.