from BBC Learning English
It's just not cricket
The phrase "It's just not cricket" is used in English to say that something is unfair or dishonest.
Examples:
I can't believe you got a ticket for the party and I didn't. It's just not cricket.
You can't copy your essay from the internet! It's just not cricket.
Diana admitted that she cheated in her A Level exams to get a place in a top university. It's just not cricket.