Creeping Oxalis - you may have come across this weed (it looks like clover). It is very difficult to remove as the crown breaks off leaving roots for re-growth. You can hand remove small plants or dig out sections where you need to if they aren't particularly large. If there is a substantial spread of Creeping Oxalis through your lawn, you will get better results by spraying your lawn with a Lawn Solutions Australia All Purpose Weed Control. Remember to maintain your lawn by fertilising and watering so that it is healthier and less prone to weed infestations.