Chasing tail

My puppy has gotten carried away with chasing his tail and has now nipped it and it has been bleeding. Now I am keeping the area clean and observing it and any issues he will be straight down the vet. But basically I'm trying to understand why he has done this and how I can stop him doing this. Thank you

Hiya! When did this behaviour begin and has it been encouraged at all? (laughing when he does it etc?) To prevent I would interrupt and distract as soon as it begins. Bug doesn't chase her tail but she does spin around in circles - usually when she's over excited or stressed and uses it as a displacement behaviour. I have seen spinning a lot in Bull Breeds in kennels - there is usually a trigger for it, this can be boredom/lacking stimulation, stress or excitement. Can you recall if he does this at particular times? Also how often is he walked/how many hours is he left each day/what do you feed him?

Well he is currently only 12 weeks old. Not been laughing at him at all when he does it but hadn't really been discouraging it (now realise I should have been). He has probable been aware of tail past 2 weeks. But only done the damage this last week. Strangely it's happened the week my husband has been of work but I have been away. He plays a lot with his toys and us and has only been going out for 2 small walks a day due to age. He had been suffering from flakey.skin skin which we put down to the food (pedigree) and we have just brought some James well beloved to try and so if that improves. When we are at work he only left for 3 hrs straight max as my husband is in and out throughout the day. He seems to do it in play so I have been offering a toy instead but as it's sore at the moment he keeps trying at random intervals. I'm going to get him a cone tomorrow as unfortunately nowhere open now