‘99 Cherokee sport starter turning over with no key in switch

Hello everyone, I’m new to the forum and need a quick answer to this madness. I’ve got a ‘99 jeep Cherokee sport I just bought last night. I was told it needed a rear u joint and the battery terminal cables, well I changed the u joint and decided I would see if the battery was just dead, so I had hooked the jumper cables up to her the first go around and all lights, radio, etc was working but I checked the starter and all the bolts and wiring was loose. So therefore I tightened everything up and gave it a second try, well when hooking the jumpers up to it she slowly was trying to roll over so I quickly unhooked the cables and disconnected the battery. Would anybody have a idea to why that would be happening?