Throw somebody under the bus
Definition 1 of 1
Pro Tip 1/3Negative Connotation
This phrase implies disloyalty and can sound harsh; use it when the betrayal is clear and intentional. 
After promising confidentiality, he threw me under the bus by revealing my secrets.
Pro Tip 2/3Figurative Language
Remember it's a metaphor and doesn't involve literal buses or physical harm. 
Figuratively speaking, it felt like she threw the whole department under the bus in that meeting.
Pro Tip 3/3Non-literal Betrayal
The phrase often refers to betraying trust or not supporting someone as expected. 
He threw me under the bus by taking credit for my project in front of the boss.