Although there is a fair amount of violence, no blood is shown at all.
The movie revolves around a test that can get a kid killed if failed.
A teen gets beaten with a stick. You can hear him screaming. Although his attacker is shown, he is not.
A masked man gets hit in the head with a fire extinguisher.
A masked man gets tackled and knocked to the ground. This results in a fight.
A masked man gets knocked out.
Multiple masked men are thrown to the wall.
Teens are forcefully pushed into chairs.
Teens are shown being beaten with a stick, although this is brief and under a red light.
A masked man gets punched by a teenage girl. The man kicks her to the ground, and is about to beat her with a stick, but he is stopped by another teen. The teen pushes the man into lockers, and knocks him to the ground. He then bangs the man's head repeatedly into the ground, although the man's head is not shown.
As a boy is crawling through a vent, the vent breaks and he falls into polluted water. To prevent him from drowning, a girl jumps in and saves him.
A teen gets hit in the face with a stick. This is shown directly onscreen, although the lighting is dim and he isn't injured very badly. After that, the attacker pushes him to the ground, and hits him repeatedly with the stick. This time, only the attacker's face is shown onscreen, with his arm swinging back and forth, stick in hand.
A man pulls out a stick on a teen. The scene then cuts to another character. It returns to the earlier shot, with the teen knocked out. The man puts his stick away. It is implied that the teen was beaten.
An adult gets punched in the stomach.
An adult gets punched in the face, which knocks him to the ground.
Two masked men get into a fight. This is not graphic, as they are in suits, and their faces are not shown.
Several teens are killed by getting poison injected into their necks. No blood is shown, and the injection is not fully shown. It is later shown that they aren't killed, but forced to work in a factory for the rest of their lives.