[2] He is the son of Jack (who was born on the Caribbean island of Curaçao) and Stephanie Seibald, and has two older sisters.
Seibald was a starter at Cornell University for its Big Red men's lacrosse team, as he attended the school's College of Agriculture and Life Sciences.
[8][1][5] As a sophomore, Seibald was one of the five finalists for the 2007 Tewaaraton Trophy, awarded to the "Most Outstanding" collegiate lacrosse player in the United States.
[1] Seibald led the Big Red's high-powered offense to an undefeated regular season, and to the 2007 NCAA Final Four.
Seibald is a five-time Major League Lacrosse All-Star, and is fifth on the all-time leader board for two-point goals.
[1] On September 9, 2009, Seibald was selected 8th overall by the Boston Blazers in the indoor National Lacrosse League draft, and was traded to the Philadelphia Wings shortly into the 2010 season.
[11] In the 2010 MLL All-Star Game skills competition, Seibald posted a world record-tying shot of 110 miles per hour.
[1] In 2012, Seibald set a career high in Loose Balls (77), while helping the Wings make the playoffs for the first time in 5 years.
[2] He was named to the team, and competed on it in the World Championships in Netanya, Israel, from July 12–21, 2018, where he scored eleven goals in seven games, adding two assists.