Indeed it has been documented in clinical studies:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6362556/
Quote:Our review suggests that increased susceptibility to ALS is significantly and independently associated with 2 factors: professional sports and sports prone to repetitive concussive head and cervical spinal trauma. Their combination resulted in an additive effect, further increasing this association to ALS.
And yet, even with the increased risk, having three teammates on the same team subsequently develop ALS is still an unlikely event. Those who play professional sports with repeated trauma are 8.5-fold more likely to develop ALS, but even with that strongly increased risk, the incidence is only about 1 per 10,000 persons per year, so most teams are unlikely to have any players develop ALS, let alone three.
BC