What advantage(s) does an ‘expert’ catcher posses over everyone else or is it something a novice lacks? From the work we are doing with children I would suggest 3 key advantages exist…
1. Prior knowledge of an effective technique and an understanding of your capabilities to execute a planned motor response
2. Pre-planning or anticipation of flight characteristics
3. Online adaptations and perception of object flight – both spatial and temporal
When watching our participants catch, the ability in first of these skills are pretty clear to see. Good catchers have a technique they are comfortable with and confident the can consistently pull off. They are aware of technical ‘tricks’ such as cupping their hands together.
Further analysis of a catcher’s movements reveal more… Good catchers appear to identify a technique that suits the task. If needs be, they can adapt this technique with practice to become more functional. The poorer catchers don’t make this adaptation. It’s like they believe in their way of catching and are going to stick with it until it works, which invariably it doesn’t.
Online adaptations are another area that poor catchers seem to struggle with. This may relate more to children with recognised motor deficits, but it would appear that these children struggle to adapt their movements once they have initiated a response. This is something that has been documented by various researchers such as Sarah Astill and Andrea Utley who look specifically at children with developmental coordination disorder (DCD).
It is possible that a child who is aware of problems with their motor coordination may feel incapable of adapting or changing their technique. This would potentially explain why they reduce the degrees of freedom at their elbows during a catch (keep them straight throughout the movement) and extend their fingers as much as possible to increase the possible surface area for the ball to land in.
Another theory to explain the lack of adaptation may be that these children aren’t aware of how they should adapt to the flight of an object. By this I mean we now know that children with poorer motor skill struggle are unable to fixate and track the ball for as long through the air, and therefore surely aren’t gaining as much information about the flight characteristics. If they have visual perceptual deficits can a child with poor motor skill gather the requirements of final temporal and spatial adjustments to enable successful interception, particularly on such a time-constrained task?
Improving Motor Control of Children and Adults with Conditions such as DCD and Dyspraxia 
I think one of the factors relating to your 3rd of 3 key advantages is to do with the children’s familiarity in dealing with the speed of the ball to execute the right spatio-temporal response. This has been seen in younger children in terms of coincidence anticipation timing (CAT) which improves with age. Ball catching for young children was made easier by either slowing down the toss or projection speed or by having the ball bounce once before the act of catching. Preference for a human tosser rather than a ball projector was also found to produce more successful catching.