There's a fundamental principle in logic called Occam's Razor. In a nutshell, it states that the simplest or most obvious explanation is also the most likely one. As this applies to Mauer's statistics, the concussion is by far the simplest and most obvious explanation for the fact that he experienced a sudden decrease in his production immediately after it occurred. Aging is far less likely to produce a sudden change like this. The same would be true for maintaining a "lazy" training regimen (which has not been clearly shown to be true, by the way). Yes, this argument relies solely on coincidence. And the reason the argument holds up is because it's the ONLY coincidence. There was no other event at the time of the decrease in production as significant as the concussion. There was no other event even close to being as significant as the concussion. Does that make it 100% certain that the decrease in production was due to the concussion? Of course not. Am I open to the possibility that there is another reason? Of course. But I think it's very highly unlikely.