When Paul O'Neill is buttoning up the jersey, he does the second-from-top button, then lowers his hands. In the next shot, he is doing up the button again.
There is a quick flash of Kramer already in the Yankees clubhouse on his way to ask Paul O'Neill to hit two home runs for the kid in the hospital (who he has not met yet) so he can get the card in return. The same quick flash is then shown after the deal is made with the kid, but the scene continues with Kramer speaking to Paul O'Neill.
When Jerry is eating the mutton, he puts the food from his mouth into his napkin, then puts that in his coat pocket. Two seconds later his clean napkin is once again hanging from his front collar.
Kramer says that Paul O'Neill that he must catch a fly ball in his hat. This is actually against MLB rules. While he can technically catch the ball in his hat, it would not be an out. It would credit the batter with a hit, and all the base runners would be awarded three bases, effectively scoring everyone and hurting The Yankees.
Elaine is supposed to be running away from dogs, but in one shot one of the dogs is running in front of Elaine instead of chasing her.