Is the bag filled and if so what is it filled with?
If it’s not something very heavy like rags or sand it will be a pointless exercise (as well as pointless exercise). The bag needs to be heavy, probably around 50kg otherwise it will swing around wildly and present no resistance to your punches (which is why it will be pointless exercise).
The ideal situation is that it’s hanging in free space with plenty of room to move around it. Even if it is heavy, with you punching it, it will still start to swing. Learning to move around the bag as it moves is part of the exericse.
We used to train on a bag at my old karate club that was filled with sand, weighed aroung 130kg and was something like 1.5m in girth. That thing was a monster and basically didn’t need anyone to hold it but you had to be so careful hitting it!
Hope this helps, I know it’s not what you were orignally asking about.