After the opening scene at the Yankees, George can be seen driving down the street in a Mercury Mystique (a vehicle used as his car in other episodes). Towards the end of the episode when George returns to New York from Akron, he can be seen driving down the street in a Buick Regal.
Kramer (Michael Richards) tells Jerry (Jerry Seinfeld) he's meeting with "Shelbig", his lawyer, yet later his secretary calls him "Shelbock." Later still, when Kramer goes to find the lawyer (Ben Stein) at his tennis lesson, he calls him "Shelback."
When George is driving and thinking about a possible comeback (at the end of the show) there's just one car far behind his vehicle but when he finally thinks of a good comeback and makes a turn back to the other side of the road, a white van appears right behind his car out of nowhere - in fact, all the vehicles in the street are different when he makes the turn.
A boom mic is visible when Jerry (Jerry Seinfeld) sees Milos (Mark Harelik) at the tennis court & realises his tennis abilities.