When the Seattle Seahawks acquired Sheldon Richardson a week before the 2017 opener, they had assembled a collection of defensive-line talent that might have been the envy of almost every NFL team. Richardson joined a pass-rush that included fellow Pro Bowlers Michael Bennett and Cliff Avril plus Frank Clark, who was coming off a 10-sack season.

A lot has changed in six months.

Bennett is gone, traded last week to the Philadelphia Eagles, and Avril's neck injury might prevent him from playing again. And the foursome that was so loaded with talent lost another piece on Friday when Richardson signed a one-year deal with the Minnesota Vikings.

It means the Seahawks have another major void to fill on their defense in addition to the one at cornerback left by Richard Sherman, but we'll get back to that in a minute.

First, it's worth revisiting the unfortunate situation that led to all of this.

The Seahawks drafted Malik McDowell 35th overall last year with visions of the Michigan State product making an immediate impact as an interior pass-rusher. But they didn't get a single snap out of him as a rookie after a summer ATV accident left him with what the team described as a severe concussion.

Richardson had been on the Seahawks' radar long before that, but they pulled the trigger on a trade when it became clear that McDowell wouldn't be available in 2017, if not longer. It remains unclear when, or if, he'll be able to play again.

In a move they probably wouldn't have made had McDowell not been injured, the Seahawks got Richardson from the New York Jets for a 2018 second-round pick and receiver Jermaine Kearse. Richardson had a year left on his contract and the Seahawks knew there was a chance he'd be too expensive to keep beyond 2017. But worse-case scenario, they figured, was that he'd sign a big contract elsewhere and put Seattle in position for a 2019 compensatory pick, ideally a third rounder.

In the meantime, he had the potential to put Seattle's defense -- specifically its front four -- over the top in a season in which the Seahawks again had Super Bowl aspirations.

It was a trade that made perfect sense at the time but one that doesn't look nearly as good with the benefit of hindsight.

The Seahawks failed to make the playoffs while finishing 9-7. As a result, the second-round pick they gave up for Richardson is considerably more valuable than it would be had Seattle been picking near the bottom of every round again.

What's more, Richardson's deal with Minnesota carries a base value of $8 million with an additional $3 million available in incentives, according to the NFL Network. That might not be substantial enough to net the Seahawks the third-round compensatory pick they were hoping to get if they lost Richardson. It might be a fourth, instead.

Of course, the more immediate concern is their defensive line.

It's not barren by any means. Clark is entering the final year of his rookie deal and could be in line for an extension. The Seahawks tendered Dion Jordan as a restricted free agent, which will keep him in the fold for 2018 as he tries to continue an NFL comeback that he started last season with four sacks in five games.

Jarran Reed, a 2016 second-round pick, made an impressive jump in his second season. And free-agent addition Barkevious Mingo figures to help out as a pass-rusher in nickel situations even if strong-side linebacker will be his primary position.

But Clark, Jordan and Mingo are all edge players. Richardson's absence leaves a void in the middle alongside Reed, and he's more of an early-down run stuffer than someone who can be counted on to consistently provide pass-rush production.

It's no wonder the Seahawks were linked to several defensive tackles even before Richardson signed with Minnesota.

One of them, Ndamukong Suh, was dining with the New Orleans Saints Friday evening, according to ESPN's Dianna Russini. That the Seahawks were apparently unwilling to match the deal Richardson got from Minnesota makes it harder to imagine them paying much more than that for Suh.

If not, the Seahawks would be left to pick from one of the mid-tier free agents that remain unsigned. Tom Johnson and Quinton Dial are two other defensive tackles with whom they've reportedly scheduled visits.

What a difference six months has made.