Cade hasn't fallen yet, instead rushing to Malcolm's defense when the Seeker is thrown. He stands over him until the latter gets to his feet again, and then prepares to rush into battle alongside him.
But somebody calls out, and for a split-second Cade responds to it. He turns his head toward Corvo and the nobles just long enough to leave himself open for several spikes of red lyrium, launched from the nearest corrupted Templar, to plunge into his thigh. He cries out in surprise as his leg gives way, and, still operating on adrenaline but becoming more and more aware of the burning pain spreading out from the wound, he holds his shield above him to deflect continued blows as he tries to make a scrambling and clumsy retreat. He finds himself pressed against the base of a pedestal sporting some stupid vase or another, and focuses mostly on shielding with the occasional stab at his assailant, who harries him in hopes of going in for the kill.
Remarkably, Cade doesn't seem too bothered by this-- at least in the grand scheme of things-- and manages to gain enough leverage that he can raise himself slightly and plunge his sword into the overconfident Red Templar's gut.
All's well that ends well. Probably.