There is no way to check the IP while you are in the game. What you can do is:
1. Ask the host via ingame chat for his ip address.
2. Exit out of the game, go back to the online game list, look for the one you were in and the ip will be on the far right.
It's annoying, I know. I'm hoping EA will add some more features to the multiplayer with an upcoming patch. Like an favorites address book, filters and the abilility to not always refresh the f'in list.
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