GBP/AUD is forming a Head and Shoulders pattern. Since the head is pointing upwards, this counts as a bearish pattern.
Support 1 is chosen since it's located at the base of the head and shoulders, reasonably conservative play.
If you're feeling lucky, consider Support 2 as a potential target. Great R/R but with a higher risk.
Another possible trade would be to wait for the pattern to complete. Let a candle close below Support 1 and ride the bearish movement towards Support 2.