“When push comes to shove” is an idiomatic expression.
Do you know what it means? Well, maybe the following will help.
1. When matters must be confronted, when a crucial point is reached.
2. At a point when, or if, all else has been taken into account and matters must be confronted, one way or another.
3. When one must commit oneself to an action or decision.
“when push came to shove, I always stood up for him”
4. When the pressure is on; when the situation is critical or urgent; when the time has come for action, even if it is difficult.
“He is not a particularly talented builder, but when push comes to shove, he can usually get the job done.”
Follow the embedded link to see synonyms for “when push comes to shove.”