fencing response fencing response the fencing response is an unnatural position of the arms following a concussion. immediately after moderate forces have been applied to the brainstem, the forearms are held flexed or extended (typically into the air) for a period lasting up to several seconds after the impact. the fencing response is often observed during athletic competition involving contact, such as combat sports, american football, ice hockey, rugby union, rugby league and australian rules football. it is used as an overt indicator of injury force magnitude and midbrain localization to aid in injury identification and classification for events including on-field and/or bystander observations of sports-related head injuries. relationship to fencing reflex and posturing