He was one of the nation's top pitching prospects before undergoing Tommy John surgery following his junior season.

[3] In July 2007, while playing for the Modesto Nuts, Nelson was named Rockies Farm Player of the Month.

On September 9, 2010, Nelson stole home plate against Cincinnati Reds pitcher Nick Masset, scoring what would be the deciding run in the Rockies' victory, their seventh straight.

[6] Though he struggled at the MLB level during the 2011 season, Nelson was announced as the third base starter along with Jordan Pacheco during Spring Training in 2012.

[18] On July 18, 2014, Nelson was called up from Triple-A El Paso and made his Padres debut against the New York Mets, going 2–4 with 2 RBI.

On February 15, 2016, Nelson signed a minor league contract to return to the Colorado Rockies organization.

[22] On March 21, 2017, Nelson signed with the Sugar Land Skeeters of the Atlantic League of Professional Baseball.

[23] He was named Bench Coach for the Northwest Arkansas Naturals, AA affiliate of the Kansas City Royals, for the 2018 season.