Blower motor only works when I take it out

it only works when I take the blower motor out, after which I turn it on and the fan starts spinning. I turn it back off at reinstall it, it’ll run for a couple days just fine then it’ll stop. I can tap the bottom of it and it starts spinning again until it doesn’t and then I repeat the process. I just want to know what exactly I need to replace. Just the blower motor? Or blower motor and fan?