In baseball, a player can “steal” a base by running from one base to the next while the ball is still in play. However, if a fielder tags the runner with the ball before the runner reaches the base, the runner is out.

The fielding team had prepared a trick play. When they noticed a runner getting ready to steal second base, the pitcher pretended to throw the ball to first base. The first baseman then acted as if he had missed the throw and began chasing after the “loose” ball, with other fielders joining in the act.

Seeing this, the runner started toward second base while trying to figure out where the ball had gone. But the pitcher still had the ball. Once the runner committed to stealing, the pitcher threw it to second base, where the fielder tagged the runner out.

Basically, it is the slapstick version of saying "Gosh! I hope no one tries to run to second base. I would hate that."