They are stuck on lead and bored, you own a basenji. If you don’t trust them off lead, get them on a long line and let them explore. They are trying to be dogs and they aren’t able to.
A over stimulated dog means you aren’t meeting it’s needs so to them “they NEED to get over to the dog across the field or they see a bird and they NEED to chase. My basenjis chase birds but come back straight after because they are stimulated and they are not desperate to get everything.
Start doing more stimulating things on walks instead of loose leading walking; you’ll find once you start meeting their needs and let them be a dog the pulling will reduce because you are providing for them.
What I do with my basenjis is bring their daily allowance of food on the walks and throw their food around in a spot and let them sniff out their food. Usually 15mins a day.
They are a sight hound and scent hound so I use a flirt pole at least twice a week and let them chase a fluffy toy
Lastly I do tug of war with them which love.
Good luck