As Football is 90 minutes long (regulation time), To avoid getting cramps in the second half of the game you, stretch, don't drink your water to fast, and keep warm if it is cold, during half time. Your water shouldn't be cold, and Gatorade and other sugary drinks give you huge cramps. Also, getting a cramp may mean you are pushing your self too hard, or that you are not in shape.
Stand up during half-time. Sitting will cause you to cool down easier. Also don't be afraid to ask for a substitution.
To help not get cramps in the middle of your soccer game eat well before the game, not greasy foods, pastas are good. Other carbohydrates, like rice or bread, are also good to eat, and lots of bananas will prevent cramps because they have potassium. And eat with plenty of time left for you to digest before the warm-ups or the game starts.
Avoid drinking soft drinks such as Coke, lemonade, etc. I once went almost a whole game and then got cramp so had to be substituted. warm up properly and you shouldn't have this problem.
As well as this buy some compression gear like skins or underarmour, it works wonders.