I feel some devious kids trying to get the lowest score possible. How to cap that? Drop all racers from the ranking that have a higher disconnection rate than 51% and that have a negative score. Just don't show their ranking.
Some numbers:
Currently approx. 3300 players are on the ranking.
300 have a score lower than 0.
525 have a higher disconnection rate than 51%.
Of course there is an overlap between these two groups.