"Ay" corresponds to the English "be verbs" am, is, are... It only appears if we use the Subject-Verb-Object structure like a usual English sentence. "Ang balbón na aso (subject) ay (be verb) hinahabol (verb) ang bola (object)" If we invert it and do the Verb-Subject-Object, which sounds more natural, "Hinahabol (verb) ng balbón na aso (subject) ang bola(object)." "ay" is no where to be seen. Now if the subject that we put in front of the verb while using "ay" is always marked by "ang" regardless of what affixes the verb used?---> Not necessarily. Because if I were to use pronouns as the subject: Ako ay aalis na. (I'm going to leave now) Kung ikaw ay artista... (If you were an actor...), "Ang" will be absurd just like "The" in their English counterparts. Hope I made it clear. :)

If you say "Hinahabol NG balbón na aso ang bola." that means " The hairy of dog is chasing the ball" Yes, true "ay" is always marked by "ang"

IS ARE IS SOMETIMES LINKING VERB OR HELPING VERBS.IT DEPENDS ON YOUR,SENTENCE..AY IN TAGALOG IS THE SAME AS IS OR ARE..IN TAGALOG SENTENCE,IN ENGLISH, THE DOER OR SUBJECT IS THE STARTING POINT OF THE SENTECE.BUT IN TAGALOG WE CAN START OUR SENTENCE IN VERB..LIKE NAGLALARO ANG MGA BATA..HOWEVER YOU CAN REWRITE IT SO THAT THE DOER IS IN THE BGINNING.ANG MGA BATA AY NAGLALARO....THE "AY" IS ADDED TO THE SENTENCE