Not trying to sound mean, but if sb calls him out on those actions and provides footage we might still be forced to take some action. We don't condone deliberate wrecking and I'm sure you understand that. No hard feelings, but maybe you can teach your sibling that proper racing can be even more rewarding than ruining other people's pastime.
Failing that a clip round the ear never did me any harm, well apart from being deaf in one ear, then being deaf in one ear never did me any harm, well there was that time I got run over as I didn't hear the damned thing but then being run over never did me any harm.