The Fencing Response: What That Strange Knockout Posture Really Means

A player takes a hard hit, goes down, and for a few seconds both arms lock into a strange, uneven position, one bent, one extended. Online, these clips usually get laughed off or turned into memes. In a hospital or on a sideline, that posture has a name, and it tells medical staff something specific about what just happened inside the skull.

What Is the Fencing Response?

The fencing response is an involuntary posture that can appear for a few seconds immediately after a moderate to severe blow to the head. One arm extends outward while the other flexes toward the body, resembling the on guard stance in the sport of fencing, which is where the name comes from. It is not a seizure, and it is not a voluntary reaction. It is a visible, physical signal that force from the impact has reached deep into the brain.

Where the Research Comes From

The fencing response was formally documented in 2009 by researchers Ashkan Hosseini and Jonathan Lifshitz at the University of Kentucky. Their team reviewed thousands of publicly available videos of head impacts, looking for a visible marker that could help identify brain injury severity in real time, without waiting for imaging or a clinical exam. Their findings, published in Medicine and Science in Sports and Exercise, showed that the posture appeared in roughly two out of three impacts severe enough to cause loss of consciousness.

Why the Brainstem Location Matters

The fencing response originates in the brainstem, in a reflex pathway called the asymmetrical tonic neck reflex. When an impact is strong enough to disrupt signaling at that level, deep in the brain rather than only at the outer cortex, the arms lose their normal symmetry and lock into that rigid position until the brain's signaling stabilizes again.

This matters for caregivers and families because it separates a genuinely serious impact from a milder one, using something anyone can see with their own eyes, before an ambulance arrives and before a scan is even possible.

Beyond Sports: When Caregivers See This

Most of the videos analyzed in the original research came from combat sports and football, but the fencing response is not limited to athletes. Caregivers in our community have described seeing the same posture after falls, car accidents, and other trauma involving a hard blow to the head. If someone you love loses consciousness after hitting their head, this is one of the physical signs worth knowing, because it can tell you something a CT scan in the first hour sometimes cannot.

What To Do If You See It

Treat the fencing response as a sign of significant head trauma, regardless of how the injury happened.

• Do not allow the person to return to activity of any kind
• Call for emergency medical evaluation if full alertness does not return within a few minutes
• Seek medical care even if the person seems to recover quickly afterward
• Tell the treating medical team specifically what you observed, since this detail is not always visible by the time paramedics or emergency staff arrive

Brain injuries do not always appear on initial imaging. The fencing response is one of the only objective, visible signs available in that first critical window, and it deserves to be taken seriously rather than dismissed as an odd reaction to a hit.

Related Reading

• Breacher Syndrome: What I Wish Someone Had Told Me, Rob's own account of blast exposure and diffuse axonal injury, the same brainstem-level force at work here
• What Causes Personality Changes?
• How to Know If You Have CTE: Signs, TES Criteria, and What Research Shows
• PTSD and cPTSD After Brain Injury: Why the Symptoms Overlap

Sources

Hosseini AH, Lifshitz J. "Brain injury forces of moderate magnitude elicit the fencing response." Medicine and Science in Sports and Exercise, 2009.

Robbins Nest Alliance is a 501(c)(3) nonprofit providing free, peer-reviewed caregiver education. If this article helped you recognize something in your own family, our free Caregiver Guide covers more signs worth knowing after a head injury. Download it here.