"The seven suspects are guilty of beating the linesman's head and upper body," said judge Anja van Holten, finding an eighth suspect innocent of the killing of Richard Nieuwenhuizen, 41.
The seven young suspects, aged 15 to 17 at the time, and the 51-year-old adult were charged with manslaughter, public violence and brutality.
"The court decides that none of the suspects had the intention of killing the linesman," the judge said.
A sixth convict, aged 15, was sent to a youth detention unit for a year with two months suspended.
The last suspect, also 15, was acquitted of the killing but ordered detained for 30 days, 17 of them suspended, because "he only hit the opposing side's goalkeeper," the ruling said.
"The conclusion is that the violence the suspects committed is the reason for Nieuwenhuizen's death," the judge said after an expert had said the death could be blamed on a genetic anomaly.