Welcome to the teenage phase!
If you are very lucky this will only last for a few days/weeks. At 9 months old my first cocker was a nightmare dog, running feral, nipping and generally being disobedient. It took this forum, a lot of chocolate and some wine (until I met up with Patp on here and then found a lot of wine helped us both with our pups
) to get through the phase....
I’d assumed that Pearl was now a fully grown dog. She wasn’t spayed until 15 months old so no hormone imbalance to contribute to the behaviour. In fact, cockers are still pups until they are the best part of 2 years old (behaviour) and 14 months old (physically - growth plates) wcs can take longer still to mature mentally and get to the right level of self impulse control needed for working (Coral is a work in progress at 4 years old).
My best advice is to go back to treating him as if he was 3 months old again. Plenty of sleep - up to 18 hours a day - short bouts of exercise/walking and mentally challenging games in between. Any poor behaviour, remove him from the room and calmly take him to his bed. Only let him out when he’s quiet and calm again. Repeat as often as necessary whilst consuming said chocolate and tipple of choice
There are quite a few pinned posts on here that will help with the mental stimulation games (how to teach a reliable recall) and lots of posts covering the same topic you’ve raised. However bad it is now, it does get better - how quickly is down to you and the consistency you and all those who come into contact with him demonstrate. If you don’t already do this, set clear boundaries such as: not allowed on furniture or only allowed up if invited, humans before dogs in doorways (gates, gaps in hedges etc) if nothing else this is plain manners and also safer for your dog. Now is the time for you to take control and show consitent boundaries so he is clear on what is expected of him.
Jayne