Hey I really like your question as analysing a sport action that requires the body parts to move in a very precise pathway is in tune with the way physiotherapist think!


THere are some quite cheap motion analysis software available over the internet that you can teach yourself to use. eg do a search for
'motion analysis software"

I am learning to use one called V1 ( i dont know wheter it is the best one available but I have downloaded a free trial version.) You use video of the persons sport action and I could imagine that you could then give your student feedback on the correct position of the shoulder and forearm. These are often used to analyse golf swings.

Having said that Its not just the mechanics of the joints and muscles that are relevant here.....you would have to consider the process of learning motor skills. This is a fascinating area of neuroscience that defy a simple explanation!