I've seen a study (that may struggle in peer review due to bias) showing the exact opposite. It will generally show that football activity doesn't lead to an increase in long term negative brain syndromes like dementia. It's a multi year longitudinal study with huge numbers and lots of controls. I'll link it once it's published.

But you should know this: the research community has basically decided that football is dangerous and are conducting studies and making editorial decisions based on that conclusion. It's a soft Lysenkoism and it's skewing the data.

There's probably a problem but because of a global warming-like bias the field is no longer doing proper research so the real consequences from football collisions alone are being overstated.

Check the papers for properly controlled populations,i.e., apples to apples comparisons to controls.