With Your Back Up Against The Wall

( restrained from acting as you would like ... )

When we are in a defensive position and have to make choices that we would not like to make, we say that we have our "back up against the wall". The wall represents an external force that causes us to act in a way that we would not like. This force may also prevent us from acting when we would like to. "I'm sorry I can't help you; I've got my back up against the wall."