Fascinating follow up
This book covers the aftermath of the release of Bouton's book "Ball Four". If you at all enjoyed "Ball Four", this follow up is strongly recommended, as it contains more fascinating detail about baseball's heirarchy and how they reacted to Bouton's book.
Without the context of the first book, many things in "I'm glad you didn't take it personally" will not make as much sense, so I strongly recommend reading "Ball Four" first so that the reader can get the maximum benefit and enjoyment from "I'm glad you didn't take it personally."