The answer is: show his friends what he likes about the competitions and invite them to come cheer him on
In this type of situation , showing his friends the situation when he competes would make them much more likely to understand his passion and realize why it is important for David to pursue it. David shall not be swayed by his friends' opinion and keep pursuing the things that he believed in.
He should Continue competing, if this is really what he loves to do and its a great physical activity then real friends would support him. These are not good friends :(
