2008-09: Steffen Soberg played youth hockey in the Oslo-based Manglerud Star program.
2009-10: Soberg made his debut for Manglerud Star in Norway's top pro league as well as playing for Manglerud's second division and U-17 squads. Soberg had a 3.65 GAA and .862 save percentage in three regular season games and 2.09 GAA and .942 save percentage in four playoff contests for Manglerud in GET-Ligaen play. He played in 17 contests in the second division and one game at the U-17 level. Soberg was chosen for Norway's U-18 squad at the Division 1 Group A World Championship tournament in Denmark but did not see any action as the back-up to Bruins' prospect Lars Volden. Norway won the tournament to earn elevation to the top division in 2011.
2010-11: Few goalies in the world faced more rubber than Soberg – both during domestic play in Norway and in international play. Handling the majority of starts for a Manglerud Star that won just 10 of 45 games and finished ninth in the ten-team GET-Ligaen, he was 5-21 with a 4.17 GAA and .884 save percentage; facing over 900 shots. Soberg played at both the U-18 and U-20 World Championships for Norway – and in both tournaments Norway was over-matched but Soberg's play stood out. This time splitting time with Volden at the World Junior U-20 championships in Buffalo, Soberg made a great first impression in his first start, stopping 36 of 38 shots in a 2-0 loss to the Czech Republic. He was shelled in his second start, lasting just over 14 minutes and allowing 5 goals on 12 shots in what ended up a 10-1 loss to Canada. Soberg bounced back in his final start, stopping 41 of 42 shots in a 3-1 win over Germany (Norway’s only win of the tournament). Soberg was impressive at the U-18 tournament, too, facing 49 or more shots in all six games. Despite losses in all but his final start (a 6-2 win over Slovakia in which Norway was out-shot, 51-18), Soberg's play created a buzz among scouts and fans as he battled waves of opposition attackers and frequently came up with big saves. He stopped 58 of 63 shots in a 5-0 loss to Canada and 48 of 51 in a 3-2 loss to the Czech Republic. Though he was not ranked among the ten European goaltenders in Central Scouting's final rankings, he was selected in the fourth round (117th overall) in the 2011 NHL Draft by Washington – the first player drafted by the Capitals.
2011-12: Drafted by Swift Current in the WHL but hoping to play in Sweden's Elitserien, Soberg instead returned to Norway's Get Ligaen where he shared the goaltending duties for Manglerud Star with 19-year-old Kenneth Sorli Eriksen. In 17 games he was 3-13 with 1 shutout and had a 3.86 goals against and .901 save percentage. Manglerud finished ninth in the ten-team league and was relegated to the second division. Soberg played in six games during the relegation series and had a 2.60 goals against and .910 save percentage. In April 2012 he signed a four-year contract to play for Valerenga, which finished second in the Get Ligaen last season.
Opinions vary widely on Soberg, who is a bit smaller than prototypical NHL goalies, played in a non-traditional hockey country, and has lost a lot of games playing on teams that were over-matched talent-wise. That being said, his play at the international junior tournaments and in his initial prospect camp with the Capitals has been impressive. He has a quick glove and uses his agility and speed to recover and make multiple saves. While there were some questions raised at the U-20 tournament when he appeared to pull himself from a game, he seemed to quell those concerns with his play for the U-18 squad.