Brock ran for George Washington Carver High School in Birmingham, Alabama, where he won the Alabama State Championships twice at 100 and 200 and once in the triple jump. His time in the 100 his senior year was the state record 10.37. Between his junior and senior years, he won an individual bronze medal in the 200 metres and was on the winning American team in the Medley Relay at the 2009 World Youth Championships in Athletics in Brixen.