http://iscoresports.com/

Do you have to enter all of the defensive players invovled in a double play to the batter and then just select double play on the runner that was the second out in the play?

Yes.

So say for example there is a runner on first and the batter hits to the short stop. Click the out button and then select ground out. Choose all of the fielders that were involved in both plays. When it asks what happen to the runner on first, click double play.

or, for common double plays, use the quick outs option by swiping up on OUT and selecting the double play that applies.