Scapular muscles play a huge role in controlling and stabilizing shoulder movement. One cannot address the shoulder without first addressing the scapulae. The serratus anterior is among the important anterior scapulae muscles. Scapular winging (i.e. sick scapula) is a condition where the scapulae medial border moves away from the rib cage (towards you if standing behind the person). Think of the shoulder blades being close together in a resting position, similar to a bird with it's wings closed. Now picture those wings 'opening up' when the bird goes to fly. When humans reach or move their arms overhead for instance only the distance between the shoulder blades should increase and NOT the distance between the ribs and shoulder blades.
This could be caused by an anterior scapular stabilization issue that could be due to a motor control problem or muscular weakness. In order to fix this movement pattern, you have to perform exercises that INCREASE the recruitment of the anterior scapular stabilizing muscles, specifically the serratus anterior. Here is a plyometric bosu ball push up exercise shown with a regression and progression (challenging for me, I need to practice this more).
According to Maenhout et al. 2016, this exercise increases serratus anterior activity in the backward push off phase GREATER than the landing phase. This is a great exercise for athletes in AND returning to sport athletes. For me I need to work my way up to the progression!
Article: Scapular muscle activity in a variety of plyometric exercises