end selection best practice

I'm designing a piece of windows software that allows a user to select items on a "canvas" (ex. will be coming up in a jiffy), and after selection somehow confirm the selection.

Context: This is a system that allows users to select different players and make a group out of them, these groups are later can be used for statistic purposes. Because not every click on the screen is for selection I added the "New Group" button on the left. The flow so far: 1. click on "New Group" 2. soccer match is paused allowing for easier selection 3. user selects x number of players (the blue dots with a white ring) 4. user somehow confirms selection

Now I have several reservations and my problem is as follows: I don't want to draw too much information on the screen since it may be much more cluttered than what we see in the image. I don't know where players will be when user selects them and I don't want to obscure any player by a "confirm" box.

For even more reference here is the image after several groups have been created and overlay information has been laid over them:

Thank you all, I hope I made myself clear enough for you to help me.