If there was something Barty really needed to work on when it came to duels, it was his problem of assuming that victory had been achieved before anyone could be absolutely sure beyond a reasonable doubt. After the Cruciatus Curse and the boils, he had been so damn sure that there was no way Marlene could retaliate that he had let his guard down again -- and even though the Tripping Jinx wasn't a particularly strong one, it was still enough to knock his feet out from under him and send him tumbling to the floor again, antennae and all. As he fell, he tried to point his wand at Marlene again and fired a Silencing Charm and Blasting Curse in quick succession, but rather more haphazardly than if his footing had been grounded.