His most lasting influence on me, and very likely the best chance for his future influence lie in his method and approach to football, which were laid out nearly in toto, in his book Finding the Winning Edge. This is why I have pasted the following two articles.
Belichick on "Finding the Winning Edge"
The first is an article about Patriots Coach Bill Belichick's appreciation of the book and of Bill Walsh's approach to the game. The article says it well. But if I could summarize, it would be that at some point, you honestly can't work harder than the other guy. Certainly not in the NFL. So what do you do? You work smarter. Both Walsh and Belichick epitomize this approach, though from vastly different starting points. Both also have three Super Bowl rings.
Bill Walsh - A Method For Game Planning
The second post is intended to give you a flavor of Walsh's approach in the form of a mid-1980s lecture he gave. Much has been said about the West Coast Offense, its origins, the pass plays it involves, the formations, the Pro Sets, the motions, the slant passes, etc.
To my mind, however, the West Coast Offense, or maybe more appropriately the Walsh Offense, has nothing to do with formations, nothing to do with routes or pass plays, and only a notional bit to do with "passing to set up the run." (As a digression, TV announcers often say that any team that throws it a bit "passes to set up the run," but when Walsh said it, he was very specific. He literally meant that he threw certain passes to certain areas to influence particular run defenders, he dropped back so he could run specific looking draws, and he would run play-action passes to set up those corresponding run plays for later in the game.)
Instead, the Walsh Offense is about two interrelated ideas: (1) A meticulous and thorough approach to building a gameplans, and (2) a calm, planned out approach to calling the actual plays in the game so that all your gameplanner is actually useful on gameday. Walsh didn't revolutionize Saturdays or Sundays, he revolutionized Sunday night through Thursdays. He figured out what would work when the pressures weren't on, he had his players practice those plays they had determined would work best, and then he actually ran those plays they practiced in the games they played, as opposed to some seat-of-the-pants calls made by other coaches.
The whole approach can be summarized by two quotes from the article below:
(1) I have been afforded the experience that allowed us to conceive an offense,
a defense, and a system of football that is basically a matter of rehearsing
what we do prior to the game."
(2) I know this, your ability to think concisely, your ability to make good
judgments is much easier on Thursday night than during the heat of the game. So
we prefer to make our decisions related to the game almost clinically, before
the game is ever played.
Unsurprisingly, one of the things that separated Walsh from the rest is that he spent a career devoted to perfecting and achieving this goal, rather than using it as a mere hope. This is what I took from Bill Walsh.