SANTA CLARA, Calif. (AP) — Chris Foerster had spent nearly two decades as an assistant in the NFL when he first crossed paths with Kyle Shanahan long before he became one of the NFL’s most-accomplished play-callers.

Shanahan was in his third year as an offensive coordinator in the NFL when Foerster joined head coach Mike Shanahan’s staff in Washington as offensive line coach in 2010 and immediately was impressed by the knowledge, creativity and teaching ability of the precocious Shanahan.

That only grew during their four years together in Washington and the past four in San Francisco where Foerster has been an assistant on Shanahan’s staff.

“I’ve been amazed since I’ve worked with him and I don’t stop doing that,” Foerster said. “It’s just how he does it and it’s just his grasp on what he’s doing.”

Shanahan’s success in San Francisco overseeing productive offenses without elite quarterback play is a reason why so many teams each January are seeking the next trendy, play-calling offensive coach to take over their teams.

All four head coaches in the conference championship games come from an offensive background with Kansas City’s Andy Reid and Cincinnati’s Zac Taylor also calling plays like Shanahan, while Philadelphia’s Nick Sirianni delegated that duty during his first season.

“Plays are just plays,” Shanahan said. “It’s how you tie them together, how you hide them, how you do things off of them and it’s how you coach them.”

Few do it better than Shanahan and Reid, whose influence on modern offenses runs deep with nearly half the teams in the NFL running offenses inspired by those two coaching philosophies.

Shanahan’s offense is based on the running game, with his commitment to sticking with the ground game leading to opportunities with play-action passes downfield.

“He’s not just copying plays from other people,” 49ers defensive coordinator DeMeco Ryans said. “He has that very creative mind and he’s always putting his players in position to make plays. That’s what sets him apart from all the other coordinators in the league.”

The Niners use frequent motion and different formations to disguise their intentions and Shanahan has created a nearly position-less offense that allows him to move playmakers such as Christian McCaffrey, Deebo Samuel, George Kittle and fullback Kyle Juszczyk all over the field to create mismatches.

“He pays attention to detail on every little thing,” 49ers rookie quarterback Brock Purdy said. “He’s the one that’s installing the plays every single day, which is pretty cool to have your head ball coach be the one that teaches you what you’re running.”

Shanahan built on the offense his father ran during two Super Bowl runs in Denver in the 1990s and has evolved it to the modern game.

He has built an encyclopedic knowledge of his system that allows him to pull plays from his past and tailor them to his current team.

Foerster also said Shanahan has the uncanny ability during a game to see how a defense is playing the Niners and will pull out a play they didn’t even practice that week.

That has led to several big plays already this season.

“He’s just looking, where’s that dagger,” Foerster said. “Where’s that play that I think will really get them on this one?”

Reid’s approach is a little different, relying much more on the passing game over his career with an offense that has hit a peak ever since Patrick Mahomes took over as QB in Kansas City.

Reid also likes to pull out some gadget plays — whether it was a play from the 1949 Rose Bowl he used against San Francisco in the Super Bowl three years ago or the “ ring-around-the-rosie” Snow Globe play against the Raiders in Week 18.

“You do (want to make it fun), but you want to score, too,” Reid said. “It’s not fun when you’re not doing that.”

The Chiefs have done plenty of that since Mahomes took over in 2018, averaging a league-best 30.1 points per game in that span — 3.6 more points per game than No. 2 Tampa Bay in a gap that’s bigger than the one between the Buccaneers and the 16th-place team.

“When you got Coach Reid, he can get anyone (open),” tight end Travis Kelce said. “He can get my dad open, if he was out there. So, I’ve been unbelievably fortunate to be under his guidance, programmed the way he is, because I do genuinely believe he does it the right way.”

Not all the head coaches still alive in the playoffs call the plays, with Sirianni having made the decision during his first year in Philadelphia in 2021 to delegate those duties to coordinator Shane Steichen.

Sirianni said that has allowed him to better manage the game and deal with defensive coordinator Jonathan Gannon and special teams coordinator Michael Clay instead of always looking at his play sheet for the next play to call.

“That’s my job as the head coach is to manage the game. Everybody does it a little bit differently, I get it, and what works best for us is that I do it this way,” he said. “We like our processes of how we’re going. We’re always trying to tweak it and make it better, but I’ve got great coaches that I’m able to lean on there, and Shane is doing a great job of calling it.”