Replaced starter and now the positive post on the battery gets really hot ?

So, one of three things are happening, either the engine is locked up so the starter cannot work, the starter you installed is defective or, the wiring is touching ground or is not connected correctly. Did the engine run before? If not, let's see if the engine can be turned over by hand, this video will help:

https://youtu.be/oN42gZN6gOE?si=69NRFWsVJTiIyXAO

Here is the correct way to install the starter and wiring. Please be careful, the battery can sometimes explode when in this condition. Wear protective eyewear and gloves. I would disconnect the battery ASAP. Check out the images (below). Please upload pictures or videos in your response of any problems so we can see what to help you with.