2008-09: Played for the Brynas J18 junior squad. In the Elit baracket, Rensfeldt played in 17 games, scoring 5 goals and adding 15 assists for 20 points. In the Allsvensken bracket, Rensfeldt netted 8 goals and added 8 assists for 16 points. He also appeared in 3 playoff games for this squad, picking up 1 assist.
2009-10: Rensfeldt moved up to Brynas' J20 squad in the SuperElit level. In 39 games, he scored 21 goals and added 29 assists for 50 points. In 5 playoff games for this squad, Rensfeldt scored 3 goals. Rensfeldt played for Swden's Under-18 squad at the World Junior Championships, where he scored 6 goals and added 6 assist for 12 points. Drafted 23rd overall by Salavat Yulaev at the 2010 KHL (RUS) Draft.
2010-11: Rensfeldt had trouble getting playing time on a young Brynas squad, though he did have 1 assist in his first 16 career SEL games. He had another dominant season in the SuperElit league for the Brynas J20 team, scoring 17 goals, 19 assists for 36 points in 26 games. He also played 11 games with Bofors in the Allsvenskan, where he notched 5 goals, 2 assists for 7 points.
Rensfeldt has the size and scoring touch to potentially develop into a power forward. He can quickly unleash his heavy wrist shot and is especially dangerous on the rush. He prefers to cut to the slot for his scoring chances rather than earning chances in front of the net. He could stand to add more strength to help fight through checks.
Rensfeldt was selected 49th overall in the CHL Import Draft by the Sarnia Sting and will likely benefit from increased ice time in the OHL for the 2011-12 season.