Bullying and adolescent group thuggery are serious problems in Indonesian schools. Your comment lists Jakarta stats, but you link is to Cikajang Garut. There were actually 3 or 4 student street brawls in Jakarta in June, one resulting in a death, but that's not as many as you suggest are common. (800 in five years is over 13 a month. That appears over blown, to me.)
Again, hand wringing, sensationalizing reports suggesting schools are unsafe does not comport with reality, in my experience. What is disheartening? The failure of schools, and beyond the local level, the Indonesian government writ large, to address this serious cultural flaw.