Richardson appeared with his fellow honorees at a ceremony at Radio City Music Hall. The award was presented by The Associated Press, which used 50 media members to vote in the various categories.
He started every game and finished with 3.5 sacks and 77 tackles, third-most in the league among defensive linemen, according to ESPN Stats & Information. The 295-pound Richardson also was used on offense, becoming the first defensive lineman in Jets history to score a touchdown and the first since William "The Refrigerator" Perry in 1985 to score two rushing touchdowns in the same season.
"I'm surprised," Richardson said. "[Buffalo Bills linebacker] Kiko [Alonso] and [Arizona Cardinals safety] Tyrann [Mathieu] definitely had outstanding rookie years. It was a toss-up to me. Kiko had a lot of tackles and Tyrann made a lot of plays. Unfortunately he got hurt. It was a close race."
Richardson became the first Jets player to win the award since linebacker Jonathan Vilma in 2004. Richardson finished with 23 votes, which edged Alonso's 19, according to The Associated Press.
"It's always nice to be recognized from the outside," Jets general manager John Idzik said, "but we already know what kind of player Sheldon is."
The outspoken Richardson wasn't shy about making his case, stating at the end of the season, "I am the defensive rookie of the year."
The first-round pick out of Missouri, chosen 13th overall -- the choice acquired in the Darrelle Revis trade -- also made news late in the season when he told ESPNNewYork.com that he'd be the No. 1 overall selection in a 2013 redraft.
This week, Richardson was called out by Hall of Famer Warren Sapp, an NFL Network analyst. Sapp, in an interview with the New York Daily News, said, "Let's not anoint this kid the next best thing since sliced bread yet."
He also said Richardson is "not that highly skilled of a pass-rusher."
Asked how he thinks Sapp would respond to him winning the award, Richardson smiled.
"I have no idea and I really don't care at the moment," he said.