[MrZeropage]

but isn't it possible then to send a 0 score or something?

no, as the procedure is like this:

you click "play game" in tournament, then the counter of tries increases by one. then you can play and if the game itself (yes, it's the game, not the arcade!) submits a result then, it is counted to that tournament-match. if you close your browser, reload the page or do anything unexpected, it could/will ruin that match.
Main problem is that only if a game provides a valid score from a tournament-game all those routines for advancing, eleminating ect. are running, that's why sometimes (in case the last result in a match is not properly saved) you need to manually advance the winner...

another problem is a user that reloads a page several times for any reason, like the "register for a tournament" page... that could possibly cause such faults.

As told before, I really never noticed something like that on the forums I technically administer