Making official a trade that was reported Friday, the Jets get a star from last season's Super Bowl but a player who is injury prone. Harvin brings versatility and game-breaking skills to the Jets, who have lost their last six games to fall to 1-6.
New York released receiver David Nelson to make room for Harvin.
General manager John Idzik called Harvin a "dynamic player who has been productive on offence and special teams." Seahawks general manager John Schneider noted Harvin's contributions to the Super Bowl and called the decision to trade him "extremely difficult."
"We are constantly evaluating our team and believe at this time that this is in our best interest to move the team forward," Schneider said.
The 26-year-old receiver has played in 60 games with only 47 career starts since being a first-round pick by Minnesota in 2009. He was traded to the Seahawks in 2013 for a 2013 first-round and seventh-round draft choice and a 2014 third-rounder.
He appeared in just one regular-season game in 2013 because of hip surgery. But Harvin ran back the second-half kickoff 87 yards for a touchdown in Seattle's 43-8 rout of Denver in the Super Bowl.
Harvin has battled a thigh injury and was listed as questionable for the Seahawks' game at St. Louis this weekend before the trade was completed. The Seahawks have tried to find ways to use him — runner, receiver and special teams — but the injury woes slowed their plans.
This season, Harvin has 22 receptions for 133 yards, with 12 of those catches coming behind the line of scrimmage. He has only one catch on a ball thrown more than 10 yards, according to STATS. Harvin's average of 6 yards per catch is last among all wide receivers in the NFL averaging at least two receptions a game.
He also has 11 runs for 92 yards and a touchdown, and 12 kickoff returns for 283 yards.
New York's offence has struggled. Harvin figures to team with Eric Decker and Jeremy Kerley as the Jets' main weapons in a so-far weak passing game with Geno Smith at quarterback.
As a rookie, he made the Pro Bowl and the Offensive Rookie of the Year. Harvin's best season was 2011, with 87 receptions for 967 yards and six TDs. He also rushed for 345 yards and two scores, and averaged 32.5 yards per kickoff return.
AP Sports Writer Dennis Waszak Jr. contributed to this report.
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