Even if violence was the way to pry the vampire off of Cap, he couldn't hit nearly hard enough at this angle, with one unbroken wrist and rapidly dwindling blood pressure. It took the knock to the head to finally have Jasper tear away, ripping a strip of flesh and fabric from Cap's leg to snarl at the interruption.
Everything was suddenly really bright, though. And really tingly; that numbness in Jasper's shoulder was spreading and when he let his mouth fall open, blood and meat falling into Cap's lap, he couldn't even feel the drool on his chin. Yawning wide wasn't stopping strange, dull ringing in his ears, either. Jasper pushed away from Cap falling back into the rubble with his eyes squeezed shut against this dizzying surge of sensations and gasping a ragged breath that caught in his throat and sent him into a spasm of choking coughing. He'd rather be hurtling through the air again.