Oooh, things could get interesting, keep us posted.
Poor Wally, some cats are bullies, when I had outdoor cats I did have some success with a hooter and a water pistol, the cat in question was an insolent nasty piece of work, (I had never met a cat I didn't like before I met him) but after a few soakings and scarings his visits did lessen, probably went to find another poor cat to pick on. Wish cats were a little more co-operative because in a perfect world Wally would gang up with the 3 new cats, beat him up & teach him a lesson.... sigh.
It is so sweet to hear that your Springer stands up for Wally.
Hope things get better soon.