As Doug Pederson’s search for the next man to live in his play-calling shadow turns into its second week, a subplot carries even more weight than his choice as offensive coordinator.

Who’s going to coach the receivers? Who’s going to coach the defensive line? Who’s going to coach the defensive backs?

The Eagles, at this moment, need practice-field teachers more than they need meeting-room schemers. If Pederson wants to save his job in 2020, he needs coaches who can hammer home technique and demand discipline. What good is the most brilliant game plan without players who can execute it? If the receivers run bad routes, the corners can’t cover, and the defensive ends never sack the quarterback, X’s-and-O’s mean zero.

Where will they find these teachers? Colleges, most likely. A lot of those interviews, and a lot of those decisions, will be made at the NFL’s annual job fair — Senior Bowl practice week, which kicked off Sunday in Mobile, Ala.

Ray Rhodes found special teams whiz John Harbaugh and running backs guru Ted Williams in the college ranks. Chip Kelly found offensive line coach Jeff Stoutland in Alabama. Those three coaches are, arguably, the three best hands-on assistants of Jeffrey Lurie’s 26 years of ownership.

What about legendary defensive coordinator Jim Johnson, you say? Or former offensive coordinator Jon Gruden? Johnson spent 17 years at colleges; Gruden, four. Even Pederson cut his teeth teaching the basics as a high school coach for four years.

The kids are the future

The Eagles weren’t golfing on Championship Sunday just because fired coordinator Mike Groh diminished the run-pass option menu for Pederson and Carson Wentz.

The Eagles were making the turn at halftime because receivers coach Carson Walch, who never coached at a major college, got next to nothing from Nelson Agholor, Mack Hollins, and rookie J.J. Arcega-Whiteside.

The Eagles were three-putting the 18th hole because defensive backs coach Cory Undlin, who also never got real major-college experience, failed to develop 2017 second-round cornerback Sidney Jones and 2017 third-round cornerback Rasul Douglas. Neither played a defensive snap in the wild-card loss to Seattle two weeks ago.

The Eagles were watching Andy Reid’s Chiefs on the TV in the clubhouse because, under the guidance of Phillip Daniels, third-year, first-round defensive end Derek Barnett ranked 211th among defensive linemen who took at least 100 snaps, though Barnett did manage a top-5 finish in one category: He tied for the fourth-highest total in penalties (eight) among all defensive linemen. Daniels’ previous coaching experience: three seasons as an assistant D-line coach with the Eagles.

All of those coaches are gone. Their principal pupils remain.

This isn’t mean to impugn those particular coaches; not completely, anyway. Undlin, in particular, was successful in his previous stops, which (incredibly) helped him land the coordinator’s job in Detroit. Walch and Daniels might thrive elsewhere. Rather, it is meant to stress that Pederson needs lieutenants who can connect with their young players and turn flashes of brilliance into consistent competence.

Jones was a top-10 first-round talent who slid to the second round only because he was injured. Douglas, large and lumbering, was projected as a safety by every franchise ... except the one for which Undlin worked. Barnett broke Reggie White’s sack record of 32 at Tennessee with 33 in three seasons, but he has just 14 sacks in three years as a pro. Arcega-Whiteside, supposedly a second-round “steal,” was cast as mini-Megatron, but with only 10 catches last season he was more like a broken Buzz Lightyear.

These are just the young players in whom the Eagles have invested the most. They certainly aren’t the only ones at crucial stages in their careers.

Practice-squad savior Greg Ward caught 28 passes in the last six games, but he still sometimes looked like a converted college quarterback. Avonte Maddox and Cre’Von LeBlanc are small, versatile defensive backs with ability but without polish. And Barnett wasn’t the only unremarkable young defensive end. Untapped potential lies in Genard Avery, Shareef Miller, Josh Sweat, Daeshon Hall, and the injured doughnut king, Joe Ostman.

Coaching is teaching, only in shorts

This isn’t meant to be an epiphany of any sort. It’s just a reminder: The most productive means to acquire top-flight coaches to teach young players is usually to pluck them from colleges. That’s because the NFL’s best position coaches either already have jobs or they’re getting promotions.

If Pederson hires well, which he has not, generally speaking, this is a stupendous opportunity for the franchise.

Imagine Pederson returning from Mobile with the next Ted Williams, who coached high school and college for 26 years before he coached Ricky Watters to his best seasons; scouted and developed Duce Staley; scouted and developed Brian Westbrook; and then scouted and developed LeSean McCoy — while turning Staley, his assistant, into the next Ted Williams.

Imagine Pederson returning with the next Jeff Stoutland, a 28-year college coach who sent Jason Kelce, Brandon Brooks, and Evan Mathis to their first Pro Bowls and turned former quarterback Lane Johnson into the best tackle in football.

Imagine Pederson returning with the next John Harbaugh — a 13-year college coach hired by Rhodes, developed by Reid, and now a Super Bowl champion head coach whose team will be among the favorites next season.

If Pederson makes hires like that this week, it won’t much matter who his offensive coordinator is.

We hear Rich Kotite’s available.