Violence & gangsterism have NO place in Singapore, a Rule of Law nation. Gangsterism is not a case of letting off steam as a one on one brawl, but it is often the case of MANY against one. Such activities can cause the loss of life, as the gangster often carry long sharp bladed bread knives which can kill.
Should one encounter such a situation, & seek to intervene, do not do so, but help by shouting as loud & as many times you can -"Ang Chia lai leow" which is in Hokkien & translated as 'red car is here now!' The red car is the much feared Singapore Police Force Special Operations Command truck which carries a large team of brutish trained armored men whose role is to stop rioting by lashing out at ANYONE, even bystanders, with batons till the rioting or fights stop. They are the only ones in Singapore whom are licensed to hurt & harm during such operations, & can't be sued, protected by legislation - an effective legacy left behind by the Brits during the racial riots in Singapore in the 60s which helped ended such activities & even gang fights.
Even feared gangsters would stop in the presence of such red truck, as they would stand no chance against the wild armored troops, even today. Most will flee in the presence of the red truck, & those who do not will end up with broken heads & bones. The troops are merciless, BUT controlled. Should a bystander see them, run as fast as possible as they will strike at anyone nearby. However should one be unable to run fast, just simply squat down & hands on head, & they will not touch you. Even present day gangsters know this rule & would throw their knives away & squat down to avoid being beaten.
Such SPF SOC trucks regularly moves around in hot spots of Singapore, thus it would not be a lie if you had shouted 'they are here', because they usually arrive within minutes in a troubled spot with calls either from the public or monitored surveillance cameras, to break up fights & save lives.