That’ll be employment rights. Look it up.
Perhaps, but it won’t be without their club, with which they have a contract, honouringnthat contract eg by paying out their contract or an agreed severance sum suitable to both player and club. Bryson, Gleeson etc are examples.
I’m afraid they are in principle. If players don’t perform well, they can be demoted out of (say) the first team squad, in which case the bonus structure for the first team squad likely won’t be available to them. Both parties may then agree to the player going on the transfer list, and may agree to a transfer to another club, terminating the existing contract. The club may offer that player an inducement to leave the club on a free transfer (Bryson).
I think the difference is that footballers sign closed contracts, ie for a specific period eg three years. In my 41 years of employment, I never had a fixed-term contract, and my experience is that that would have been unusual. I was obliged to heed contractual notice periods, however, and was never fortunate enough to have an employer say to me “Just **** off then, and we’ll pay you for your notice period”. I was ever the model employee, of course.