1) You are such a big fan that the thought of opening your mouth or taking your concentration off the game makes you feel nauseous. They will respect this level of concentration.
2) Every football team has a different formation but the most common theme, particularly in International football, is 4-4-2. That's 4 defense, 4 midfield, and 2 strikers up top. Look at which player is in which position, if you think one of them is drifting into another position then shout "get back!" or "push up!" This is an adequate level of observation and should show that you have some knowledge.
3) I live in NYC and watch a lot of football here (British MCFC fan) so please, whatever you do, NEVER cheer for a throw-in. Americans tend to do this at the pub, and it makes most football fans cringe.
4) If someone misses an "easy" goal, shout: "My grandma could have scored that!" Note, if someone has already shouted this, then don't bother.
5) Constantly complain about how much you hate International football, you find it too slow, one dimensional, and cagey. This will show you have a deeper understanding of the game.
6) Feel free to shout "Defense," but do NOT shout "Offense!" You may replace offense with 'attack,' 'push up,' or a general, loud "come on" should suffice.
7) When you are watching the game, it's called "football"!
If you are still in doubt, then just keep buying your friends drinks, and they'll soon forget that you've been lying to sound cool.More questions on football (soccer):