Suppose you are walking on a public land and there are no legal restrictions to you doing it.
Suddenly someone appears on your way and says you can't walk here. They are not a law enforcement officer but simply a person who (falsely) believes they have the right to stop you (like they believe they own the land and, on top of that, that they can physically remove you).
You try to make your way anyway, but they physically do not allow it (like obstruct the way and make it impossible for you to pass unless you push them out of the way).
Would you be allowed to use some minimally necessary force to make your way? Like push them out of the way, and if they start to fight, fight back to keep them away? Let's assume force is used carefully e.g. you won't push them down a cliff, won't specifically aim to hurt them etc.
This question is inspired by this article (where a squatter has occupied "abandoned" council-owned land with public walking tracks and claims ownership), but is not tied to that specific case.
Bonus question: what offense does the bully commit?
In case this question seems easy, here is an enhancement: let's assume that you need to go where the bully doesn't let you to, or someone will die (e.g. you are going to render first aid to someone seriously injured).
Answers re any jurisdictions are welcome.