Assassinating Roger Federer doesn't seem to be a very good threat. He always comes across quite well and difficult to dislike in contrast to some other tennis players I will not mention.
But they are hoping it is only an oral threat!
Plus he's Swiss, they generally don't do much to merit being assassinated
He's a tennis player, and a pretty high-profile one; if you're going to exterminate tennis, its as good a place to start as any.
I think there are other sports I would rather exterminate than tennis. American Football - just don't get it!