9. Nick Blackwell (2016)
Blackwell was his own worst enemy. The British boxer became a professional despite having no amateur experience. Despite this, he achieved success and eventually met Chris Eubank Jr. in a British Middleweight boxing clash. However, Eubank got the better of the fight and inflicted severe swelling upon his opponent. The referee suffered the fight and an ambulance rushed Blackwell to the hospital.

Doctors diagnosed him with bleeding inside his skull and put him in a medically-induced coma. After a week, they brought him out of a coma but warned him never to fight or even spar again. But Blackwell didn’t listen and continued sparring in the gym. He received a stiff blow to the head and underwent an operation to reduce swelling on his brain. He didn’t respect the vulnerability of his health due to his life-threatening injuries, but luckily he recovered from this.