2010-11: Robert Hagg played for Tierps HK men’s team in lower Swedish hockey as a 15-year-old, skating in 30 games for the East coast club, and played for MODO’s U18 and U16 teams. He scored 2 goals with 9 assists and had 30 penalty minutes for Tierps HK. He was scoreless with 2 penalty minutes in two U18 games for MODO and scored 2 goals with 13 assists and 26 penalty minutes in eight games for MODO U16. Playing for Uppland in the TV-Pucken tournament for Swedish high school players Hagg led all defensemen with 4 goals with 5 assists in eight games.
2011-12: Hagg moved to MODO for the full season, spending most of the year with the U20 squad, and represented Sweden in the 2011 U19 World Junior A Challenge and 2012 U17 World Hockey Challenge tournaments in Canada. In 52 games for MODO U20, including eight playoff games, he scored 5 goals with 14 assists and was plus-11 with 48 penalty minutes. He played six games for MODO U18; scoring 1 goal with 4 assists and was minus-one. Hagg was scoreless with 4 penalty minutes at the WJAC and scored 2 goals with 4 assists and had 16 penalty minutes in six games at the WHC.
2012-13: Hagg split the season between MODO’s Elitserien and U20 Super Elit league teams – playing in 27 games with the men’s team and being named the top Super Elit defenseman. He played for Sweden in the 2013 U20 and U18 World Junior Championship tournaments, serving as an assistant captain on the U18 squad. Hagg had 1 assist and was minus-three, averaging 7:46 minutes of ice time, in Elitserien regular season play. Seventh place MODO played Farjestad in the playoffs but Hagg did not see any ice time in the five-game series. Hagg scored 11 goals with 13 assists in 28 games with MODO’s U20 team during the regular season and played for both the MODO U20 and U18 teams in the playoffs (both of which won silver medals). He also won a silver medal with Sweden at the U20 WJC scoring 1 goal with 1 assist and was minus-one in five games. Sweden’s U18 team reached the quarterfinals and in five games Hagg scored 1 goal with 3 assists and was plus-one with 12 penalty minutes. Hagg was ranked eighth amongst European skaters in the Central Scouitng final rankings and was selected by Philadelphia in the second round (41st overall) in the 2013 NHL Draft.
2013-14: Hagg signed a three-year entry-level contract with the Flyers in March 2013 after skating for MODO in the SHL; making his AHL debut with Adirondack at the end of the year. He skated for the Sweden U20 team in the 2014 World Juniors. Hagg scored 1 goal with 3 assists and was plus-1 with 10 penalty minutes in ten games with the Phantoms. Adirondack missed the playoffs; finishing fourth in the Northeast Division. Hagg scored 1 goal with 5 assists in 50 games for MODO and had an even plus/minus with 49 penalty minutes; averaging 13 minutes of ice time. In the two game play-in series against Linkopings he was minus-1 with no points and 4 penalty minutes. Hagg scored 1 goal and was plus-4 with 12 penalty minutes in seven games at the WJC. Sweden won a silver medal; falling to Finland, 3-2 in overtime in the championship game.
2014-15: Hagg skated for Flyers’ AHL affiliate Lehigh Valley in his first pro season in North America and was an assistant captain for the Sweden U20 team at the 2015 World Junior Championship. He scored 3 goals with 17 assists and was -12 with 42 penalty minutes in 69 games for the Phantoms. Lehigh Valley finished fourth in the East Division, missing the AHL playoffs. Hagg had 2 assists and was -3 with 2 penalty minutes in seven games for Sweden at the WJC. Sweden finished fourth, falling to Slovakia in the bronze medal game.
2015-16: Hagg skated in 65 of 76 games for the Lehigh Valley Phantoms in his second AHL season. He scored 5 goals with 6 assists and was -11 with 42 penalty minutes. The Phantoms finished seventh in the Atlantic Division, missing the AHL playoffs.
Hagg is generally sound in most aspects of the game, but doesn’t have any dominant traits nor has he been consistent in his effort, which plagued him in his first AHL season. He keeps things simple, but can sometimes miss assignments in his own zone and a choppy stride prevents him from controlling the play on the rush. He can play the point on the powerplay, and he makes a sound breakout pass. He has a great frame, is not shy of the rough stuff, and looks like he can be molded into a punishing defender.
Hagg spent his second season with the AHL's Lehigh Valley Phantoms in 2015-16. Still adapting to the game in North America, the 21-year-old gradually assumed more responsibility with the Phantoms as the season progressed. With prospects Travis Sanheim and Ivan Provorov expected to turn pro in 2016-17, Hagg must make strides in his third season to remain relevant in the Flyers' plans. He projects as a sound, two-way defenseman.