It was one evening in May this year that the alarm came about an injured man between Rosvalla and Nyköping's high school.
The man had been stabbed and the police drew up a report of a suspected attempted murder.
Later, a now 19-year-old man was arrested on suspicion of the crime.
The heading was later changed to aggravated assault.
The 19-year-old himself has denied the crime, and said that he stabbed the man in self-defense.
But the district court instead follows the prosecutor's line and on Thursday sentenced the 19-year-old for aggravated assault and minor drug offenses to probation.
Two other young men have been acquitted of suspected involvement in the assault.