more info: https://en.wikipedia.org/wiki/1987_Campeonato_Brasileiro_Série_A
I researched some Brazilian sports and legal websites about this.
The Federal Supreme Court of Brazil (Supremo Tribunal Federal STF) was called and, incredible as it may seem, they denied Flamengo's appeal and kept Sport as champions in 1987.
Source: STF nega recurso ao Flamengo, mantém Sport campeão de 1987 e São Paulo com Taça das Bolinhas
STF mantém Sport como único campeão brasileiro de 1987
The STF (Supreme Federal Court) resolving issues about football is the face of Brazil. I understand the merit, but the situation and the arguments about who gets which title are quite funny.
They should never have taken legal action in this case, that's what sports justice is for... Now imagine if this becomes a pattern? all the teams that feel unfairly decided to take legal action... This is Brazil. zil zil...
Anyway, I think this Sport title is very unfair, because the CBF was unable to organize the 87 championship, which was the responsibility of the club of 13... And we all know the end of the story.
Yes, it really is something very unusual to see and something very Brazilian. But I think that if many teams follow this path, they will act to avoid this type of discussion as there is no point in discussing titles in court.