pin something on somebody/something phrasal verb ( see also ↑ pin )
1 . to blame someone for something, often unfairly:
Don’t try to pin the blame on me!
They’re trying to pin the murder on the boyfriend.
2 . pin your hopes/faith on something/somebody to hope that something will happen or someone will help you, because all your plans depend on this:
Chris is pinning his hopes on getting into Yale.