Complex sentence: By the end of the season, Larsson had tied the single season record for scoring in Elitserien among defensemen under the age of 18, a record that was set by Tomas Jonsson in 1977--78, who compiled 8 goals and 9 assists in 35 games.
Split into simpler sentences: By the end of the season, Larsson had tied the single season record for scoring in Elitserien among defencemen under the age of 18. The record was set by Tomas Jonsson in 1977--78, who compiled 8 goals and 9 assists in 35 games.