Harrison was a 2009 SC/NC Select All-Star and a 2008 and 2009 Beaufort Gazette/Island Packet Baseball Player of the Year.  He was named to the South Carolina AAA All-State team, and was rated no. 5 best high school player in the state of South Carolina by Diamond Prospects.  

Harrison finished the 2009 season with a 10-1 record and a 1.53 ERA with 82 strikeouts.  He pitched four complete games and had two shutouts.  He played 2009 summer baseball on the 18-U Carolina Cyclones AAU team and 2008 summer ball on the 17-U Diamond Devils team that won the 17-U World Wood Bat Association National Championships, as well as the Continental Amateur Baseball Association 18-U Wood Bat World Series.  Harrison was also named the MVP of the 2008 Continental Amateur Baseball Association 18-U Wood Bat World Series.