In combat sports such as boxing, kickboxing and mixed martial arts, a fighter's chin is the ability to tolerate physical trauma to the head, in the form of concussive or sub-concussive blows, without being knocked unconscious or severely disoriented.
Fighters are said to have a "weaker chin" if they exhibit limited ability to absorb punishment to the head before they are severely impacted.
Many analysts have observed that the ability of a fighter to absorb blows to the head without loss of consciousness can be affected by the process of weight cutting.
Weigh-ins for competitors usually take place the day before competition meaning that the athletes may not be fully hydrated by the time of their contest.
This can reduce the amount of fluid surrounding the brain, exacerbating the damage caused by blows to the head.