He may be able to see his reflection in the glass and think there is another beardie close or your temps could be too hot check the temps and make sure they are alright!
What I did about the reflection thing was put printer paper on the inside of the tank on the sides and i cant move my backdrop to the inside rear glass but it is recommended. When I put it inside on the sides of the glass it seemed to make him relax a lot more and only scratch when he wants to get out mostly!
If you really think about it though all he/she is doing is getting exercise by running on the glass lol eventually they get tired mine does anyway!
Well,ok I will check hid basking tempd later when I turn on his lights buthow kan I get him bulky again,he lookd skinnyto my compared to my,other dragon wich is younger an way fattrr
Check out the care sheet in my sig below. Make sure you are feeding a good staple and feed often. They can eat an amazing amount of food. Wax worms are a good treat to add some weight to beardies. But, the care sheet has some good info on feeding. I recommend reading that part. There is also a good link to a nutritional chart for beardie foods. Make sure to check that out and see if what you are feeding is a good feeder.