dirty pool

English

Probably an allusion to failing to follow the rules when playing billiards. Compare not cricket.

dirty pool (uncountable)

(slang) Foul play, misconduct, underhandedness.
- 1967 April 21, Keith Wheeler, Sandy Smith, “Murf the Surf and his Jewel-studded Jinx”, in Life, volume 62, number 16, page 95:
  The thieves, in their turn, have developed a self-pity syndrome about the FBI, considering government surveillance to be dirty pool — unjustifiable interference with free enterprise.
- 1984 December 15, Meryl Altman, “Irresponsible Coverage”, in Gay Community News, volume 12, number 22, page 4:
  To call Harriet Pilpel "strident" because she clearly and knowledgeably opposed Brownmiller's (and Cottingham's) position is not only dirty pool, but obfuscates the issues and prevents GCN readers from having access to Pilpel's well-defended and logical reminders that […]