I was reading elsewhere and wish I had the link, but the theory was the build up of rosin and sweat and rosin and sweat can create a ‘sticky substance’ situation. I think that’s why the umpires had him wash his hands, because a legal substance, overused, was having an affect of an illegal substance. But after being questioned a second time about it, and then letting him continue to pitch, without washing his hands again, I do question that.