2009-10: Hargrove played in ten junior games with the NAHL's St. Louis Bandits after splitting the season between the Dallas Stars U18 and St. Louis Amateur midget AAA teams. He had 2 assists and was an even plus/minus in four games with the Bandits during the regular season and scored 2 goals and was plus-one with 6 penalty minutes in six playoff games. In 16 games with the Dallas Stars U18 team he scored 5 goals with 6 assists and had 16 penalty minutes. He skated in 30 games for the Amateur Blues and had 14 goals with 10 assists and 72 penalty minutes.
2010-11: Originally selected by Indiana in the 2009 USHL Draft, Hargrove was obtained by Fargo in a trade and spent his first USHL season with the Force. Hargrove supplied physical play and was fifth on the team with 27 points as the offensively-challenged Force finished fifth in the Western Conference. In 56 games he was third on the team with 109 penalty minutes and was plus-nine with 13 goals with 14 assists. Fargo reached the second round of the USHL playoffs and in five games Hargrove was plus-three with 3 assists and 2 penalty minutes.
2011-12: Hargrove once again provided crunch and some scoring in his second season with Fargo. He led the Force in penalty minutes (140) and was the team's third-leading scorer. In 54 games he scored 16 goals with 22 assists and was plus-one. Fargo finished fourth in the Western Conference and advanced to the second round in the playoffs. Hargrove was scoreless in six playoff games and was minus-one with 10 penalty minutes. He committed to playing college hockey at Western Michigan in 2012-13. In his third year of draft eligibility, he was selected by Boston in the seventh round (205th overall) of the 2012 NHL Draft.
The Bruins have been focusing on adding toughness in the draft and Colton Hargrove is a great example. The tough Texan is a power winger who loves to hit and grind in the dirty areas. Heavy on the puck down low and tough to move from in front of the net, Hargrove is well suited to the pro game. He also has surprisingly good hands and feel for his linemates, though his bread and butter is certainly his power game.