not cricket - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Unfair, unsportsmanlike, as in It's not cricket to let him go without notice. This term, in which the sport of cricket is equated with upright behavior, survives in America despite the relative unfamiliarity of the sport there. [Mid-1800s]