How long do babies keep their fists clinched before its abnormal?

Baby's fists: By about 6 months, a baby's clenched fist usually disappears.

About 4 months: At birth a babies hand easily moves into a clenched fist as a reflex.They do not actually have control of the clinching, which can be frustrating to women as they grab hair when held up near it. The fisting subsides as they begin to have the ability to open it (2-3m) and then grab & release by 3-5m. Constant fisting after that time would be considered abnormal.