Problem, imagine you've found an amazing fishing spot that someone has inconsiderately gone and put a wall of trees or cliff face against. In other words you've got no space for the back cast! Solution, we call it the roll cast.

This cast must be practiced on water as it relies on the surface tension between the water and line, and it just wont work on grass.
The roll cast is nothing more than one forward cast, executed perfectly. You cannot roll cast for a large distance, so make sure that you get as close as possible to the target before starting. Spool off as much line as you need into the water in front of you. The closer your arm is to the surface of the water the better, so either wade into the water or go into a crouch.

Raise your rod-tip to the 2 O' Clock position behind you and allow the back-end of line to be raised off the water's surface. Let the line develop a little slack and then perform the forward cast exactly as normal coming to a complete halt. What should happen is that a loop will form and roll along the length of your line. If you stop the forward cast close to the vertical, the entire line will lift off the water and straighten, allowing you to drop the line exactly where you want it to be.

Technique

How do we place that line with the minimum of effort? Firstly, the shorter your fly line, the easier this is to do. So, try and creep up as close as possible to your target. As mentioned before, the shorter your line, the easier it is to cast, and if your casting isn't up to scratch, neither will be your placement Once you have mastered the false casting, backwards and forwards about 3 times, let the line drop and start again.

It is very important that you last false cast be NO DIFFERENT from the previous false casts. Just because it is your “last cast”, it doesn't change the laws of physics. So your last false cast is coming up. Rod stops dead at 10 or Two O' Clock (Depending on which direction you're casting). Wrist holds steady. Line flies over your shoulder straightens and…...drops. As the far end of the line starts to fall FOLLOW IT DOWN with your rod. Let your rod drop at the same rate as the line. In that way the whole of the line will land gently and at the same time. Even better let your whole body go down to the ground, until you end up on your haunches.

The important points here are to follow the line with your rod and to not change your action of your last false cast. The most commom problem found here is that your last cast did not stopped at the correct position and the line splashes into the water right at ones feet, or runs out of steam halfway through the cast and lands in an untidy heap in the middle of the water