Lay summary – Repeated knocks to the head, including some traumatic brain injuries, may increase the risk of brain problems later in life. This study looked at donated brain tissue to see whether people with a history of repeated head impacts had changes linked to a brain condition called CTE. The researchers also looked for changes in a protein called TDP-43, which is often involved in brain diseases. They found that this protein was not more common overall in people with repeated head impacts, but when CTE changes were present, the protein tended to affect more areas of the brain. This research may help scientists better understand how repeated head impacts can affect the brain over time.