Though I've never witnessed an attack, we have friends who have, and they said it was utterly amazing how adept Blue Jays are at avoiding capture.
Due to the Hawks size, they don't have the maneuverability as smaller birds do, so in the case of the Blue Jays, our friends mentioned how the Jays stayed safely in the tree, staying completely calm, and hopped from lower branch to higher branch, lib to limb, again and again, until the Hawk moved on.
I would have loved to witness such an event.