Ask Farmer: Why do teams script their plays, like the 49ers’ First 15?

Have a question about the NFL? Ask Times NFL writer Sam Farmer, and he will answer as many as he can online and in the Sunday editions of the newspaper throughout the season. Email questions to: sam.farmer@latimes.com

How does it work when teams script their first 15 or so plays and the execution of some of the plays goes awry? When something goes wrong along the way, are the ensuing plays altered? Is there a Plan B and C?

Carter LeClair, Marina del Rey

Farmer: The late Bill Walsh, Hall of Fame coach of the San Francisco 49ers, is widely credited with coming up with the practice of scripting the first 15 offensive plays of the game. In fact, the 49ers coined the term “First 15” in reference to that play list.

For some background on the whys and hows of the First 15, and how it might be altered in the early going of a game, I turned to Hall of Fame quarterback Steve Young and Lowell Cohn, author of the 1994 book “Rough Magic: Bill Walsh’s Return to Stanford Football.”

Cohn said Walsh’s practice of scripting plays evolved from the first five, to first 10, and finally First 15, and the reason for its doing so was “purely diagnostic.”

“He would test the defense in various ways,” Cohn recalled. “I know this because I would sit and watch film with him.

“When he was at Stanford, he showed me what he had done against USC his first year. I don’t remember the play, but he said, ‘I tested this guy.’ And what he was looking for in their secondary was, how would the cornerback react, what coverage would they rotate to help the cornerback? And now he knew it.

“And he would come back to that cornerback and use that knowledge against USC. Or against the Rams or whoever.

“It’s not that he would forget which plays to call. There was a specific reason, a progression so he could learn about the defense and use it against them.”

Young’s recollection of the scripts is they were more about the 49ers than the opponent. He said it was rare for the 49ers to get all the way through the scripted First 15.

“Its primary purpose was to put people on notice the night before — ‘This is what we’re doing. This is where we’re headed. These are the things we’re going to be dialing up,’ ” he said. “It just got people focused on tactics and a plan.

“If we ran through the First 15, great. If we got three in, and all of a sudden it was third and 15 and all heck breaks loose, then everybody knew … it wasn’t a cause for alarm that we didn’t run through the First 15.”

Young said that when the First 15 plays were released each week, certain players would snap them up and devour them like a high-schooler checking out a new yearbook.