He probably suffers from Chronic Traumatic Encephalopathy (CTE); also known as dementia pugilistica or "punch drunk syndrome." I say probably because the only way to confirm this is through a pathologist after death, and even with an autopsy, it is sometimes confused with Parkinson's. This disorder is very similar in symptoms to Parkinson's but is caused by external trauma (or repeated concussions) instead of genetic predisposition.
Parkinson's Disease
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