Colin Kaepernick’s chaotic workout on Saturday has left a trail of controversy — and sources told Page Six that a host of behind-the-scenes issues include a letter Kaepernick wrote in 4th grade, legal arguments over a workout waiver, and even a pissed off Jay-Z.

Controversial Kaepernick was meant to workout for NFL teams on Saturday in Atlanta, but minutes before the QB was to take the field at the Falcons’ training complex, his reps said they’d moved the session 60 miles away to a local high school. (Eight teams showed up, and Kaepernick appeared in a T-shirt that read, “Kunta Kinte,” in reference to “Roots.”)

The stunned NFL then released a lengthy statement on Saturday with a flurry of details, including a claim that Nike wanted to be at the workout to turn it into an ad. (The brand launched a Kaepernick commercial last year that garnered controversy, a sales boost and a Creative Arts Emmy.) Said the NFL on Saturday, “Last night, when Nike, with Colin’s approval, requested to shoot an ad featuring Colin and mentioning all the NFL teams present at the workout, we agreed to the request.” But Nike then said it did not have cameras at the workout, and just wanted permission to use the names of NFL teams.

Page Six has learned exclusively that while Nike wasn’t filming, it did have a marketing move up its sleeve — in the form of a branded congratulations to be posted to Kaepernick. The marketing material — seen by Page Six — consists of a letter that Kaepernick himself penned back in 4th grade when he dreamed of having a job in the NFL. “A Note from Colin Kaepernick, 4th Grade,” says the copy, followed by kid’s hand-writing in pencil that reads: “I’m 5ft 2 inches 91 pounds. Good athelet [sic]. I think in 7 years I will be between 6ft – to 6ft 4 inches 140 pounds. I hope I go to a good college… then go to to the pros and play on the Niners or the Packers even if they aren’t good in seven years.” The letter by young Kaepernick is signed, “Sincerely, Colin.” It then has the “Just Do It” tagline, and a list of all the teams that were to be at the NFL’s workout. A Nike rep did not get back to us.

A source huffed of the concept: “Saturday was his big day, and on Friday night [before the workout], you’re thinking about your Nike ad? The whole thing’s just a commercial.” But another source insisted: “It is simply not true that Colin, with Nike’s approval, requested to shoot an ad the night before. There was never discussion of an ad or commercial. There was some contemplation of Nike sending a congratulatory post the day of.”

It’s now unclear if Nike will use the 4th grade letter in its materials.

Either way, Kaepernick used the workout as an ad of sorts when the former NFL star debuted a pair of Nike Air Force 1s on the field, which he’s created for the brand.

Yet another heated disagreement we hear was over a liability waiver that the NFL wanted Kaepernick to sign prior to the workout — and whether the waiver was “standard” as the NFL said, or “unusual,” according to team Kaepernick. The league said on Saturday that, “On Wednesday, we sent Colin’s representatives a standard liability waiver… At noon today, Colin’s representatives sent a completely rewritten and insufficient waiver.”

Kaepernick settled a collusion grievance against the NFL this year. One source close to the league told us, “there was nothing in the waiver that had any bearing on the claims [Kaepernick] was making in his collusion grievance. It was a standard liability waiver… to prevent a player from claiming entitlement to worker’s compensation if there was an injury. Colin’s reps told the NFL that they had minor edits… and that Colin understood the need to sign a waiver. None of the points that were raised [on Saturday about the waiver] were ever mentioned previously.”

But another source disagreed by saying, “The NFL said their waiver was ‘based on’ [a standard liability agreement]. That’s like saying a skyscraper is ‘based on’ a hut. It was not standard language.” Kaepernick’s reps apparently replied with a different standard physical injury waiver that’s used by local Atlanta colleges for physical injury, and “rejected the unusual release that potentially waived Kaepernick’s employment rights,” a source said.

Other issues included whether Kaepernick would be allowed to film the workout — which the NFL wouldn’t allow, but said it would instead give his reps raw footage.

After the chaotic switch of venues, some who had been in Kaepernick’s corner were left questioning his tactics. “People were working so hard saying to the NFL this is the right thing to do. In reality it was the wrong thing to do. It was a fiasco,” one source lamented. But another source said, “There were dozens of issues thrust upon [Kaepernick] to address in 72 hours… Typically a quarterback would script this for weeks. If they truly wanted to help him they would have said, ‘Let’s pick a date. We can make this perfect and they wouldn’t have rejected transparency of having an independent camera crew or the media film the workout.”

One person watching the situation who was not pleased, we hear, is Jay-Z. A source told us on Sunday, “Jay-Z feels disappointed with Colin’s actions, and believes he turned a legitimate workout into a publicity stunt.” Jay Z has a partnership with the NFL through his Roc Nation label, and reportedly pushed for the league to give Kaepernick the workout.

Meantime another source fired back, “at the end of the day [the workout] proved that Colin is an elite quarterback who should be starting in the NFL.”