[RCMcKenzie]

His Christian, or given name, is James Laurie White. His parents and friends probably called him Jimmy, Jim, Jaime etc. Baseball players have a long-standing tradition of giving everyone a nickname. They called him "Deacon".

A Deacon in the Catholic church is a member of the congregation who is from the community. They are not formally trained like the priests, but they read from the bible and stand on the stage with the priests during the ceremony. Often, Deacons in a Catholic church are Bankers or Lawyers during the week and participate in the Mass on Sunday.

My thought is if they called him, "Deacon", they thought he was overly pious. And if he drank in his later years they may have called him McCreachery to make fun of his pious ways and beliefs (flat-earth) etc. At the same time, he was the manager and one of the winningest players of the era and so they respected him.

I am only speculating here, and preferred the title "story" to "theory" as I have very little fact to support my conjectures.