Sources: Chiefs agree to trade quarterback Alex Smith to Redskins

— -- The Washington Redskins and Kansas City Chiefs have engaged in the first blockbuster of the 2018 offseason. The Redskins will acquire quarterback Alex Smith, ESPN has confirmed, allowing them to part ways with previous starter Kirk Cousins.

The Kansas City Star first reported the trade, which can't become official until the start of the league year on March 14. The Redskins would give Kansas City a third-round pick and Redskins cornerback Kendall Fuller as compensation, sources told ESPN. ESPN's Adam Schefter and Chris Mortensen also reported that Smith would sign a four-year extension with the Redskins, averaging $23.5 million per year with $71 million in guaranteed money.

Fuller is the player that made the trade for Alex Smith possible, according to Schefter. The Chiefs view Fuller as a bona fide starter, to go along with the third-round pick they're receiving.

Fuller apparently didn't get word he'd been included in the deal before that detail was leaked. A series of Fuller tweets went from saying he was trying to find out, to saying he wasn't in the deal, before lightheartedly posting how he felt after finding out.

At least six other teams expressed interest in Smith, according to Schefter.

The move likely gives Washington a cheaper alternative to Cousins at quarterback. Cousins is a pending free agent and made it clear that he did not want to strike a deal before free agency began. During multiple appearances on Radio Row at the Super Bowl Tuesday, Cousins reiterated what he had said all along this offseason: He would wait to see if the Redskins tagged him by the March 6 deadline before deciding what would come next.

But a third franchise tag would have cost them $34.5 million and the transition tag would have cost them $28.8 million. Now, Cousins can hit free agency and the Redskins will receive a third-round compensatory pick in 2019. The fear for Washington was that paying Cousins perhaps more than $25 million per year would have handcuffed them in making other moves.

The Redskins have approximately $52 million in cap space available for 2018. It's uncertain yet how much Smith will cost against the cap in 2018, but it will be cheaper for Washington than tagging Cousins.

Signs have pointed for some time that the Chiefs would trade Smith, their starting quarterback since he was acquired in 2013. Last year they traded up in the first round to draft Patrick Mahomes, who looked ready to become a regular in the one game he started this season. The Chiefs also need some salary-cap relief and would save $17 million by trading Smith.

Smith, 33, came to the Chiefs in a 2013 trade that sent two second-round draft picks to the San Francisco 49ers. He not only stabilized what had been a shaky position for the Chiefs -- seven different players started a game for the Chiefs at quarterback over the six seasons prior to Smith's arrival -- but he guided the team to the playoffs in four of his five seasons. The Chiefs won the AFC West in each of the past two seasons.

But Smith was only 1-4 with the Chiefs in the playoffs and couldn't guide them past the divisional round. The Chiefs scored just 16 points in their 2016 playoff loss to the Pittsburgh Steelers and were shut out in the second half of their postseason defeat against the Tennessee Titans last year.

The Chiefs last year drafted a quarterback, Mahomes, in the first round for the first time in 34 years. That signaled the beginning of the end of Smith's time with the Chiefs.

Smith responded with his best NFL season. He was the NFL's top-rated passer with a 104.7 rating and set career records with 4,042 yards and 26 touchdown passes.

Smith spent the first eight seasons of his career with the 49ers. He was having at the time his best NFL season in 2012 when he was benched late in the year in favor of Colin Kaepernick. The 49ers went on that season to the Super Bowl with Smith as a backup.

The 49ers drafted Smith with the first overall pick in 2005.