Hitting the squash backwall boast or desperation shot
You should try to get this shot into the corners of the court still - It takes some time to get it but maybe you could practice it a few times . If you hit it in the middle of the court your opponent has too many options. Either that or you are just too slow....
Squash Jersey writes
The goal would be to hit the with a sharp upwards trajectory so that it floats high enough so that you can get back to the T. ... If it goes into the middle your opponent has the advantage. The best thing at that point is to anticipate what your opponent will do with your loose shot.
Anyway, it is afterall - "a desperation shot" and so you've forced another shot from your opponent, which may be worthwhile. I would agree with JB on his point... it's not a good shot... but sometimes it's the only alternative.
What you want to create with this shot is a high lobbing ball that hits the front wall softly and quite low with a ton of backspin on it. If you can also place it into the front corner where it adds side wall constraints to your opponent all the better.
The glass surface puts more spin on the ball than the walls which make it much different than hitting a similar lob off of the front wall. There are other major obvious differences between the two shots such as a rebounding ball versus one that is moving towards the wall that require very different timing. These differences aside, the way to get the maximum touch and back spin you want is to wait as late as possible to strike when the ball is only about a foot or less perhaps from the backwall. In this position you can hit the very steep angle you need to get the desired backspin, but the ball makes contact fairly low on the back wall allowing the running length of the high arch of your shot to be proportionally longer than the rise.
You may also be surprised at how much less power is necessary to carry this shot when it is made closer to the wall. When executed properly, the ball rises and falls in a graceful arch brushing the front wall a foot or two above the tin and subsequently dropping almost dead as it pulls itself towards the sidewall and into the floor. It requires lots of practice to get it right but knowing the technique should help a lot.
The somewhat difficult, backspin backwall boast, is easiest to make effective if hit straight. Of course the cross corner has the advantage of also making the short bounce into the sidewall. But it is also a longer and thus a slower shot that not only has to be hit with more skill which also gives your opponent a little more time to adjust and handle the surprise. There is also a 3-wall and 4-wall version of the backwall crosscourt boast that is consistently easily aimed shot fired tight into the backwall/back-sidewall corner. This shot must also be taken close to the wall and with a bit more power to make up for the losses to the secondary contact. When mastered it can produce some interesting dynamic results. It takes a fair amount of practice to get your body/feet in position to make a clean shot at the right angle with sufficient power. It will truly make you smile when you execute your first good one and you see the look on your opponent's face.
You should try to master the straight shot first though, as it is the most effective when hit very high with all the backspin that makes it bounce real short. If your opponent has a big swing prepared he will have to adjust to hit up on the low bounce to clear the tin. To practice, hit a few over-long drives with a good warm ball on your backhand side and then follow one in close to the backwall with your forehand, with a real open face on your racket. (Trying to practice by bouncing a ball off the backwall won't give you the contributing energy of the ball moving towards the wall, the close proximity needed to hit the shot correctly or the relative timing of turning and hitting a ball traveling in the same direction.) If you are up to it, try to go to the front and return your own ball.