Dubois, the 26-year-old British heavyweight, delivered a fifth-round low shot to Usyk, the Ukrainian unified heavyweight champion.

He criticized Dubois for not capitalizing on his physical advantages and suggested that Dubois needs to work on his heart.

Russ Anber lays out the rules around boxing's low-blow laws and explains why Daniel Dubois' controversial shot on Oleksandr Usyk was illegal.