When you're using a crowbar to lift a large rock, you are working against the force called
[tex]\boxed {\bf Gravity}[/tex]
[tex]\bf Explanation:[/tex]
Gravity on Earth is what gives weight to all objects, it's defined as all things that have mass or energy are gravitated towards each other. Therefore when you're using a crowbar to lift a large rock, the weight is caused by gravity.
I hope this helps you!