From Longman Dictionary of Contemporary Englishstab somebody in the backstab somebody in the backBETRAYto do something that harms someone who likes and trusts you SYN betray → stab
Examples from the Corpus
stab somebody in the back• I see, you criticize my appearance, and then you stab me in the back!• Some one reached through an open window and stabbed Bastidas in the back.• Thatcher was stabbed in the back by her former friends and colleagues in the Conservative Party.• Why stab Manchester in the back for helping to create a bigger northern network of clubs, raves and fashion outlets?• He seems friendly, but he wouldn't hesitate to stab you in the back if he thought it would help him get your job. 