The way Biden could knock Trump off balance is something that would cause him to retort with an attack on Biden personally. Remember, Biden has the “media” well in his corner, and they will manipulate sound bites to favor him.
The greater point here is Biden has a very, very low bar to cross. If he is at all lucid and holds his own, he will be declared the “winner.” He should not be taken lightly.
The New York Times have already written their front page story declaring Biden as the winner of the debate. Same as they did for Hilary. Three times. Fake news media declaring Biden the winner won't impress anyone or change any minds. No one really believes CNN etc anymore. Not even the Dems who watch CNN.
As far as throwing anyone off balance is concerned, its Trump who is going to go after Biden on that. Just mention Hunter Biden taking that $3.5 million from the wife of the mayor of Moscow and trafficking in women and Slow Joe will start squealing like a stuck pig.