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The first day of the NFL's 2015 league year opened with the most unusual and intense scene imaginable: Three blockbuster trades almost completely unseen just minutes before.

There was a time -- oh, about two years ago -- when trades were a rarity in the NFL. Tuesday, in about 10 minutes' time, we saw the St. Louis Rams and Philadelphia Eagles swap quarterbacks, the New Orleans Saints unload tight end Jimmy Graham and the Detroit Lions find a replacement for defensive tackle Ndamukong Suh.

Why so many trades? Let's sift through that and other takeaways from Day 1 of the NFL's free-agent market.

• NFL general managers used to limit player trades in part because of salary-cap implications. When a player is traded, the prorated portion of his cap figure -- mostly his signing bonus -- accelerates into the current league year. In some cases, that acceleration created an intolerable cap hit for a player no longer on the roster. Over the past two years, however, the salary cap has risen by $20 million. Surplus cap space is easier to find. Plus, teams have found other ways to limit proration in long deals. Long story short, trades are much less prohibitive now from a salary-cap perspective. Many of us want to attribute Tuesday's deals to a new generation of swashbuckling general managers, which might be true in some cases, but the trend has a more tangible base than that.

• Here's a secondary reason that trades have become more popular: When the opening bell rang Tuesday, the NFL announced 453 players on its official list of free agents. Based on records kept by ESPN Stats & Information, that's the lowest total since 2009. (There were 477 last year.) Teams are no less interested in adding players this year, so they have pursued other avenues amid the shrinking pool.

• The unexpected retirement of quarterback Jake Locker is another hit to a woeful 2011 draft class. Think of it this way: Locker, Blaine Gabbert and Christian Ponder were three of the top 12 picks of the first round. Gabbert re-signed Tuesday night with the San Francisco 49ers, where he will compete to back up Colin Kaepernick, but he has no chance to start in a league starved with mediocre quarterback play. Ponder is a free agent and isn't expected to re-sign with the Minnesota Vikings. The obvious lesson: Find a way to draft the quarterback you like instead of drafting the best quarterback available when your pick arrives.

• Cornerback Darrelle Revis cemented his credentials as a pure football mercenary by leaving the Super Bowl champion New England Patriots for a superior offer from the New York Jets, who have missed the playoffs in four consecutive seasons. As a result, Revis has a chance to be the highest-paid non-quarterback in NFL history. Per Spotrac.com research, Revis earned $85.2 million in his first eight seasons. His agreement with the New York Jets will pay him $48 million over the next three years, bringing him to at least $133.2 million and as much as $155.2 million if he plays the duration of the deal. At the moment, according to Spotrac data, the richest non-quarterback in NFL history is defensive end/linebacker Julius Peppers ($138.4 million). Of course, Suh could eclipse Revis, Peppers and the rest of the field with the $114 million deal he is expected to sign with the Miami Dolphins. (The deal had not been officially announced as of late Tuesday night.) Suh has already earned $64.2 million in his career.

• While we have a moment, let's tally what the Lions paid to lose and replace Suh. First, they will absorb $9.7 million in dead money against their 2015 salary cap. Next, they sent their fourth- and fifth-round draft picks to the Baltimore Ravens for Suh's replacement, Haloti Ngata. They'll pay Ngata $8.5 million in the final year of his contract and either need to extend his deal or risk losing him after one year. The Ravens sent Detroit a seventh-round draft choice to complete the deal, and the Lions will probably get a 2016 compensatory draft pick as well. So in total, the Lions lost one of the NFL's best players, gave up two draft choices and will devote $18.2 million in 2015 cap space to the position in exchange for a declining (but still productive) player and a likely compensatory draft pick plus another throwaway choice. That's paying a premium to correct a mistake.

• The number of agreements that apparently occurred during the three-day "legal tampering" period preceding free agency has drawn NFL scrutiny. In the scheme of NFL problems, this one doesn't seem too high. But here is an aspect of the three-day period that blows me away: Teams can't speak directly to the player, much less host him on a visit, until the period expires and free agency begins. So the Dolphins, for instance, committed $60 million in guarantees to Suh without ever speaking to him directly about his long list of on-field antics. The Chicago Bears committed to signing linebacker Pernell McPhee (five years, $40 million) without discussing their new plans on defense with him. How much due diligence could a team possibly perform without a face-to-face -- or even phone-to-ear -- discussion?

• The Patriots frequently have been noted for cutthroat personnel decisions during the era of coach Bill Belichick. Over the years, they have replaced still-productive cornerstone players from Richard Seymour to Wes Welker to Logan Mankins. But let's not sell the Seattle Seahawks short in this regard. In consecutive years, they have parted ways with a key part of a Super Bowl team. In 2014, they showed little interest in re-signing veteran receiver Golden Tate, clearing the way for them to make Percy Harvin a bigger part of their offense. Tuesday, they inserted popular center Max Unger -- a starter for the past six seasons -- into the package that brought Graham from the Saints. Seahawks coach Pete Carroll's genial personality does not inhibit him from cold personnel decisions.

• Tuesday's frenzy left at least one sizable story untold: How will the Minnesota Vikings' standoff with tailback Adrian Peterson end? Peterson met Monday with Vikings ownership and has now had face-to-face meetings with all of the decision-makers in this process. All anyone can do is guess at this point, so here's mine: If the sides had an agreement for Peterson to remain with the Vikings in 2015, we probably would have heard by now. It still appears, from afar, that Peterson is trying to convince the team to give him something new -- either a new contract or a fresh start. My guess is the team would be more likely to facilitate the latter than the former.