It WAS his own blood
In my post above, I opined that it was silly, not that the main issue was whether it was or wasn’t his own blood, it was what kind of benefit would a baseball player derive from it.
People may not like a “pretty boy” like Tom Brady, but he was trying ways to extend his career with diet and exercise, and doing it in a sport where real physical contact for a 40+ year old athlete was a going concern.
But, for this baseball player...it is him and his money, and it isn’t illegal.