2010-11: Adam Ollas Mattsson played for lower division club Varmdo HC in the Stockholm suburb of Gustavsberg; appearing in games with the club’s U20 and U18 teams as well as playing for the U16 squad.
2011-12: Ollas Mattsson skated for Djurgarden in the top division of Swedish junior hockey, played for the national U16 team and was part of the bronze medal-winning Stockholm 1 team in the TV-Pucken tournament for high school players. He was -1 with no points nor penalties in his only game with Djurgarden’s U18 team and was +8 with 4 assists and 6 penalty minutes in eight games with the club’s U18 team. He was +5 with 1 assist and 2 penalty minutes with Sweden’s U16 team. Ollas Mattson was +12 with 2 goals, 1 assist and 4 penalty minutes in eight TV-Pucken games.
2012-13: Ollas Mattson played his first full season with Djurgarden — skating for the club’s U18 team — and represented Sweden in the 2013 U17 World Hockey Challenge in Canada. He had 8 assists and was +32 with 44 penalty minutes in 32 regular season games for Djurgarden and was +4 with 1 assist and 6 penalty minutes in eight playoff games. He had 3 assists and 26 penalty minutes in six games at the WHC. Sweden defeated Russia, 7-5 in the gold medal game.
2013-14: Ollas Mattsson represented Sweden in the 2013 Ivan Hlinka Memorial Tournament in August before returning to Djurgarden and finished the season skating in the 2014 U18 World Juniors. He skated in six Allsvenskan games with the Djurgarden men’s team; spending most of the season with the club’s U20 squad. He had 2 assists and was +3 with 4 penalty minutes in Allsvenskan play. Ollas Mattson scored 1 goal with 8 assists and was +2 with 42 penalty minutes in 33 games in the U20 SuperElit regular season. Djurgarden finished ninth in Top 10 play, defeating Skelleftea in a preliminary series before being swept by Farjestads in a best-of-three quarterfinal series. Ollas Mattsson had 2 assists and was +2 with 2 penalty minutes in four playoff games. In four games at the Ivan Hlinka Tournament he was +4 with no points and 2 penalty minutes. Ollas Mattsson scored 1 goal with 2 assists and was +2 with 4 penalty minutes in seven games at the WJC. He was ranked 15th amongst European skaters in the Central Scouting final rankings and was selected by Calgary in the sixth round (175th overall) in the 2014 NHL Draft.
Ollas Mattsson is a tall defender with good weight and some real snarl. He has held his own playing against men as a teenager and relishes physical play in solving problems and handling defensive situations in his zone. He puts his long reach to good use, constantly bothering opposition attackers. Ollas Mattson plays a sound positional game and shows no hesitation in blocking shots. He has a decent first pass with an aptitude for blueline play. The offensive game doesn’t yet appear to be the strength but he is good at keeping pucks in the offensive zone and blocking passes. He was set back by an injury in his draft year and is still fairly raw as a prospect. Olllas Mattsson has shown weaknesses in foot speed and concentration, making his fair share of errant and/or poorly chosen passes.
Ollas Mattsson made his debut in Sweden's top league in 2014-15, skating for Djurgarden in the club's first season back in the SHL after its promotion last spring. Averaging just under 11 minutes of ice time in limited action with Djurgarden, and also playing for the club's U20 team at times, Olla Mattson has at times struggled due to a lack of mobility. It is an area that will need to continue to improve if he is to eventually compete successfully in the SHL and then make his way to North America. Long-term he has potential as a classic shutdown defender but must continue to improve in all areas to one day skate in the NHL.