The New York Jets defensive tackle beat the Buffalo Bills linebacker and Arizona Cardinals safety to the league's defensive rookie of the year award.
The 23-year-old told ESPN: "I'm surprised. Kiko and Tyrann most definitely had outstanding rookie years and it was a toss-up to me.
"Kiko made a lot of tackles and Tyrann made a lot of plays down the field. Unfortunately he got hurt, but it was a tight race."
Richardson made 77 tackles, 3.5 sacks and a forced fumble in his debut season.