cliché — an expression, idea, or element of an artistic work which has been overused to the point of losing its original meaning or effect.
No matter how many times I advise a player to “watch the ball”, it doesn’t stick. They continue to look at the front wall when their opponent hits the ball. I believe that it is not a natural behavior to watch someone hit a projectile at 100+ mph in ones general direction. There is an instinctive reaction for self-preservation, regardless of the cool eyeguards one is wearing.
Intellectually, the benefits of watching the ball at all times should outweigh the fear of getting hit by the ball. If you are watching your opponent hit the ball, you immediately know if you are directly in the line of fire (or in the cross court path). With this knowledge, you can take evasive action and get out-of-the-way.
If you are watching closely, you can also tell if your opponent is hitting an offensive or defensive shot. If they hit the ball at shoulder height or above, then expect a ceiling ball. By keeping your eye on offensive shots hit at knee level, you can more easily follow the path of the ball on the way to the front wall.
A Tactical Game
So how do you overcome instincts. One way is to prove that something bad will happen if a player does not watch the ball. So I suggest playing a tactical game where if a player catches their opponent looking at the front wall at the moment they hit the ball, they can stop play, and win the point.