You can never entirely remove subjectivity because it will always feature in things like the degree of force and dangerousness of a challenge.
One thing would be in offside where you could say that only a player that touches the ball can be offside (but this would potentially lead to tactics like people standing right in front of the goalkeeper to block his view).
You could remove subjectivity from handball by simply saying that any contact with the hand or arm was always handball. Again that might have some unintended consequences but at least it would be simple and consistent.
As passionate about my own team, much less bothered about other football