It's no wonder Sergey Kovalev's nickname is "Krusher". Of his 30 victories, 26 have ended in knockouts. The Russian's journey to success hasn't been all highs, however. Early in his career, he had to endure the death of one his opponents caused by their fight just three days prior. Sergey says it almost ended his career, but has since managed to return to fighting and hasn't lost since.