Why did Jack Dillon appear to decline so rapidly after 1915?

He still beat Levinsky several times in 1916 as well as Gunboat Smith, and what at the time was a huge victory over Frank Moran and still had some good wins in 1917. Its not like he totally fell apart but his decline was steep and it was probably a combination of factors. He had been fighting for almost ten years by the time 1917 rolled around and had a huge amount of fights in that time. He started fighting as a lightweight and by the time he moved up to light heavyweight he not only had a lot of mileage on his odometer but he was also fighting above his best weight for a guy who was only 5'7" He also suffered from puglistic dementia while he was still very young and some stories have him already suffering the early signs as early as 1921 so its entirely possible, given the progressive nature of such brain damage, that he was already slipping from it as early as 1916/1917.

 

I think they were still good wins but I make the point in my book on Greb that Dillon was probably beginning to decline by the first and certainly second fight with Greb. That being said, even prior to the first Greb fight Dillon had drawn with HW Tom McMahon and beaten Jack McCarron, George Chip, and Len Rowlands, all good fighters. Whether Dillon fell apart over night before, during, or as a result of his fights with Greb, Gibbons, et al is anyones guess but after that point his slip was precipitous and he was no longer the guy who set the midwest on fire in the early 1910s.