2019 Hong Kong anti-extradition bill protests

A mob of suspected masked triad members dressed in white and armed with batons attack commuters indiscriminately at Yuen Long station, injuring 45, including a pro-democracy legislator and a pregnant woman. Hong Kong police have been accused of allowing the violence to happen due to their delayed response and decision to limit emergency services in the area.

'Where were the police?' Hong Kong outcry after masked thugs launch attack

Sources:  SCMP  The Guardian