By Jon Wertheim In our latest mailbag, we look at Canadian tennis’ recent slump, the legacy of Steffi Graf and Nick Kyrgios’ recent behavior. First: much respect to Mark and Ken. This is the wildest recreational tennis story you will hear. And before we get to the mailbag, here’s An Ode to Clay by reader Fernando: What is Clay? It is tactic. It is point construction. It is defense. It is consistency. It is perseverance. It is stamina. It rewards the serve, but not disproportionately. It is rallies. It is creativity. It is athleticism. It is innovation. It is determination. It is perseverance. …