It goes partway down reverses direction and goes back up again.
Garage door closes then reopens.
If it closes only partway the safety sensors are usually responsible clean the lenses or realign them and make sure there are no obstacles blocking the beam.
This is almost always the result of a dirty or obstructed safety feature.
Your garage door is programmed to travel a certain distance before it closes.
If you re craftsman chamberlain etc garage door opener is closing and then opening up its likely a common problem related to the stop limit mechanism.
If it closes before that distance has been traveled it thinks something is wrong and it reopens to help prevent any damage or safety risk.