I keep getting questions pop into my head today, why do cricketers 'rub' their cricket balls down the side of their groin prior to bowling (it leaves an awful red mark on their whites too) ????? I have always thought this very strange....but rude ! lol....
Keeping one sie polished (And the other side rougher) forces the air over the ball to go at differing rates and makes the ball move from left-to-right or vice-versa, depending on what the bowler wants it to do.