There are a lot of research studies done on jump mechanics. It can tell us a lot of different things. Jumping with wrong mechanics is a risk factor for an injury, not ideal for performance, may indicative of insufficient muscle strength, etc. The athlete may be compensating, not feeling comfortable jumping, or scared.
There are so many things that we look at when evaluating jump mechanics. We look at it from the front. We look at it from the side. We look at how much the knees and hips are bent when they land. We look at where the feet re pointing, etc. One thing that we evaluate when looking at the athlete from the front is where their knees are when they take off and when they land. The pictures below are showing a basketball players jumping to a box. Her knees are almost touching each other when she takes off.
Also, we can tell that she is leaning towards her right leg which is her healthy knee. She is rehabing from a knee surgery and has good quads and hamstrings strength and training her hip muscles as well as balance, squatting mechanics, etc. So, why is not jumping the right way?! She may not be able to use her muscles, or she is so used to jumping this way for a long time, or there are other potential factors that her jump mechanics is not the way it should be. Whatever the reason may be, as a rehab professional, we need to find out why and fix this because we know, from the past literature, this is not a good sign and this may predispose her to another injury in the future.