How to cheat at sport

I have previously considered the cliché move the goalposts but what about the oft-demanded level playing field? We all know what is meant by the phrase, but I cannot think of a sport where a sloping playing field would disadvantage one team.

Take football. If your team finds itself on a playing field with a distinct slope towards their goal, you can relax in the knowledge that the second half will redress the imbalance when the teams change ends. In any case, surely it would have to be a really significant deviation from the horizontal to make a difference?