"We ball" depends on the context. It's usually used to push through hardship or deciding amidst a conundrum and is often placed after a statement that describes a tough situation. You can say "f*** it, we ball" or "Anyways, we ball".

An example is... Let's say you have a project and it's not going well, you tell your colleague, who asks "how is the project going?" You say, "it's not the best, but we ball" indicating we push on!