A Super Combo Blitz is earnt by hitting multiple combos in a row without hitting other fruits in between.
This can only be earnt in Arcade mode,and the best time is just after activating the Frenzy powerup.
Once that powerup hits, aim to hit as many small combos as you can in a row (hitting smaller combos means there is more fruit left for other combos - Just keep hitting combos in a row until the achievment unlocks.).
This may take quite a few goes, so just keep trying.