Sign of the Cross

We see a football player score a touchdown and then kneel down and make the sign of the cross. A baseball player makes the sign of the cross before he steps into the batting box. A basketball player makes the sign of the cross before shooting a free throw. What are they actually doing by making the sign of the cross? This is not just a Roman Catholic thing. I have seen the sign of the cross done in Episcopal, Anglican, Lutheran, Presbyterian and Methodist Churches. This video I have recently watched explains it all very well.