Yes, naively the connection looks like head impacts. The high rate of concussions in soccer is not widely appreciated, despite being over half the rate of American football (about which a lot more has been written).

https://storelli.com/blogs/the-storelli-blog/soccer-concussi....

https://journals.lww.com/cjsportsmed/Abstract/2001/10000/Con...

From the first link, here is the ranking of concussion rate:

1. Rugby (4.18/1,000 AE) 2. Ice hockey (1.20/1,000 AE) 3. American football (0.53/1,000 AE) 4. Lacrosse (0.24/1,000 AE) 5. Soccer (0.23/1,000 AE) 6. Wrestling (0.17/1,000 AE) 7. Basketball (0.13/1,000 AE) 8. Softball & field hockey (0.10/1,000 AE) 9. Baseball (0.016/1,000 AE) 10. Cheerleading (0.07/1,000 AE) 11. Volleyball (0.03/1,000 AE)

> Athletic Exposure (AE) is defined as one athlete participating in one game or practice.

Football and soccer players both. I'm pinging on agro chemicals--from the mentions earlier. I have to assume all natural fields are heavily treated (herbacide and insecticide) and that players spend or have spent their early career on natural fields. All of these chemicals are derived from "nerve agents" that mess with proteins in the central nervous system...or so it is my understanding.

I believe the eyes are a vector for prion diseases, at least some.

Possibly infection when being looked at for a head injury, but I assume they take decent precautions.

Another user proposed grass was the commonality between those sports, in that case grass/dirt entering the eyes?

For forest/streams, possibly water/dirt entering the eyes?

Doesn't really narrow much down though, avoid all dirt, grass, and water.

I‘m not sure I‘m buying the prion theory. Shouldn’t numbers decrease as people go outside ever less often? Prevalence of ALS seems to be increasing though: https://www.ncbi.nlm.nih.gov/labs/pmc/articles/PMC6735526/

I think the Borrelia Burgdorfferi hypothesis would fit better, with Lyme disease numbers climbing in recent decades.

And yet Lou Gehrig played baseball.