Boxer Patrick Day died on Tuesday, days after suffering a traumatic brain injury during his match for the USBA super welterweight title in Chicago on Saturday. The 27-year-old fighter is now the fourth boxer to perish this year from injuries sustained in the ring.

In July, two boxers — Maxim Dadashev, a 28-year-old Russian, and Hugo Alfredo Santillán, a 23-year-old from Argentina — died of brain injuries they received in fights. Dadashev died on July 23, four days after his light-welterweight fight in Maryland, while Santillán died five days after he collapsed following a fight in Buenos Aires.

Then, in September, a Bulgarian boxer named Boris Stanchov died in the ring while fighting under his cousin’s boxing license in Albania, the Washington Post reported.

This latest wave of fatalities has highlighted the intrinsic dangers that come with boxing, giving fuel to the case made by proponents that the sport should be banned.

At the very least, some argue, boxing organizations should implement safety protocols such as adding padding to gloves or shortening fights to lessen the chance a fighter will leave the ring with brain damage or a traumatic injury such as the one Day experienced in the 10th round of his fight.

Although the brain is shielded by a thick skull, the brain itself is only as firm as jello, UCLA professor of neurology, Christopher Giza, explained to Brain Facts. When someone is hit hard enough to render them unconscious, the brain can experience permanent damage as it rattles inside the skull.

“That twisting and pulling can cause brain circuits to break, or lose their insulation, or get kinked up, and that shuts off parts of the brain,” he said. “If the part of the brainstem responsible for consciousness is affected, then you would be knocked out.”