The "when the guy owns the ticket" part is a question of title.
Let's take a gander at yon UCC, which covers these questions in most cases in most of the US.
https://www.law.cornell.edu/ucc/2/2-401
Blah blah blah blah. I'm too lazy to read all the stubhub fine print again, but last time i did, it said nothing. That means, in circumstances like these, title passes to buyer when physical delivery of goods occurs.
That's when the buyer owns the tickets.
The rest of the questions are pretty standard breach of contract and damages questions, which others seem to have covered.
Here, the buyer would definitely have recourse against the seller (but probably not against stubhub).
Of course, stubhub is being stupid in this case too, there are a variety of mechanisms it could use to prevent this from happening (escrow, charging sellers difference in current price vs old price if they reneg on tickets that have gone up more than, say, 100% in price, etc). Sadly, it looks like Stubhub also has a financial incentive to let this happen, since they make 20% of the price.