<This post popped upnon 'active' but I typed a reply before noticing it was not the main forum. Advice sent with good intentions, OP.>
Your update refers to your husband's 'heated' competitive behaviour. What does this look like? Is your child's response reflective of this? Whilst enthusiam, drive and determination are important, competitive sport is no place for hostile aggression.
I would encourage your child to look at the many successful athletes who are competitive whilst demonstrating self discipline and control. Disappointment and frustration will occur but managing these feelings is vital.
• Karim Benzema - no red cards in over 900 games.
• Gary Lineker- no red or yellow cards in over 600 games.
• Roger Federer - well known for his calm composure even in high pressure games.
Fines for conduct are given to those who can't control their temper. You will easily find examples of athletes fined, banned or disqualified even in elite events online.
You have written he is a high achiever in sport but this will not be the case if he can't control his anger, shouts, storms off and is aggressive especially to younger players.
There are plenty of books and online guides for regulating emotions/big feelings. You can read them together and talk about how he could react differently. His actions are his responsibility and are within his control.
He needs to manage his emotions in the moment using a method that works for him such as breathing techniques, counting to 5 or tensing and relaxing.
You can turn this into a positive step towards success. Focus on the positives. Find a positive role model in your son's competitive sport and encourage him to follow their lead. Let him become an athlete with success and a positive career record.