A 43-year-old man was assaulted near Helsingborg’s Olympia stadium before their first game of the campaign, at home to Djurgardens.
The man, who has not been named but is from Stockholm and believed to be a Djurgardens fan, was taken to hospital but later died from head injuries.
Fans of the away team invaded the pitch at half-time, chanting “murderers, murderers” at the home fans, before the match was called off.
"I can confirm that a person has died at Helsingborg Hospital. He was brought there after an incident at Karntrappan in central Helsingborg," police spokesperson Ewa-Gun Westford said.
“It is a sad day. It is extremely tragic for this man’s family, for football and for the whole community,” Helsingborg sports director Jesper Jansson told the TT news agency.
“Any sporting consequences of the game are completely overshadowed by this tragedy.”
Police moved swiftly to deny that the man was involved in hooliganism, telling newspaper Aftonbladet that the man was not known to them in relation to football violence.
Djurgardens' sporting director Bo Andersson said: "He was no hooligan. He was an ordinary supporter, a father of four who liked to go to football."
On Saturday five people were hospitalised following a brawl between rival fans ahead of the match. According to local police, three arrests were made and 33 more men were temporarily held in custody for that incident.
The traditional pre-match fan march that marks opening-day games in Sweden was also marred by violence, as away fans rushed home supporters on their way to the stadium.
Sweden has an unusually high level of crowd violence for a nation with one of the lowest crime rates in the world.
Fans regularly clash at games in a league which can sometimes attract relatively large crowds, including pockets of self-styled 'ultras', who mimic Italian supporters in their behaviour.
Former Helsingborgs striker Henrik Larsson, one of Sweden's most celebrated players, expressed his sadness at the incident.
"What the hell are we doing?" he asked reporters after his own Falkenberg side lost 3-0 to Malmo.
"That's not why we go to football, it's f***ed. Should we have a league like that? It's about time we started taking some responsibility for what happens at football.
"Look at Malmo today - it was like a party in the stands. That's how it should be."
- Sports & Recreation