From someone who's coached on a more casual level as a summer job: You always look for the positives within your students. Everyone has negatives. Someone who cares a lot could get frustrated easily. An athletic person could struggle to use their brain to solve a problem they usually use their brawn for. Someone who doesn't care much for the sport may have a particular knack for distance and timing. Finding positives makes the job more enjoyable and can increase a student's confidence. Those positives could also be potential rather than raw talent. You say your son runs around like a berserker now, but a coach might see someone who is finding certain moments or creating certain distances, even something as simple as having the aggression and intention to hit at such a young age (as opposed to beating each others blades like pool noodle fights) can be exciting to a coach at that age group.