Here are a few articles on croquet that I have written over the years..

For umpires:
 How can a croquet player detect a double hit? A research report. 

For referees:
Home study course to help you become a croquet referee in Australia
Changes to the laws in 2008
Understanding Law 27, especially 27(e) to (h)
 Fallacies about the laws

On croquet history:

Isaac Spratt, a forgotten pioneer of croquet Some records of Australian croquet history can be found in England

On possible changes to the laws:
Do the rules of golf croquet and the Association game have to be so different?