No problem with this one.

This delivery is clearly legal as the bowler's entire front foot is behind the popping crease.

Remember the umpire has also to keep an eye on what the back foot is doing as well.

Still a fairly straightforward decision for the umpire as the bowler has kept around half his front foot behind the popping crease.

But the official still has little time to make up his mind before he switches his attention to the other end.

This shows how difficult it can be for the umpire.

This delivery is legal because some of the foot is behind the popping crease.

The fact that the foot is raised does not make it illegal.

This again shows how tough no-ball calls are to make.

This is a no-ball as none of the foot is behind the crease.

Unlike some other sports touching the line does not count.

This should be a relatively straightforward call - it's a no-ball.

But as the Old Trafford Test showed it is still all too easy for the umpire to miss as he tries to concentrate on the business end.