Rules are important to clarify - but it shouldn't be so hard as some are making out to simplify some things. Free kicks are punishments or rewards, depending on which end you're on, so like anything, it's all about incentives.
If the "line" is drawn in the wrong place, you'll see one of two very obvious behaviours start to manifest:
- If the line is too harsh: there'll be an epidemic of players deliberately trying to "draw" the free kick (diving/ducking/flopping/shrugging/acting) - playing for a free kick becomes a better option than continuing to actually go for the ball.
OR
- If the line is too lenient: there will be an epidemic of infringements with players getting away with it (eg: constant holding off the ball, throwing, dropping etc) - infringing becomes a better option than playing by the rules.
By getting the balance right, it saves having to endlessly add clauses to each rule.
For example, with high tackles:
A couple of years ago you would often see players duck their head, shrug their shoulders, or raise one arm in attempt to "draw" a high tackle free kick. It became so wide spread that the league decided to intervene. That's a clear indication the incentives are out of whack - that the line is drawn in the wrong place.
It had become "worth it" for a player to risk getting hit high, because the players evaluated that the benefit of getting the free kick, outweighed the cost of getting hit harshly in the head (and the humiliation of being labeled a ducker). The intervention should have been simple: move the line for what is interpreted as a high tackle, so that if you enter a tackle with the goal of receiving a high tackle free kick - you'll actually have to put up with a significant knock to the head - the natural remedy for anyone who wishes to "play" for a free kick.
Instead the league complicated the rule by adding clauses. This has complicated the interpretation: did he duck, did he shrug, was he just down to pick up the ball or did he deliberately stay down a bit longer? There's now a page of criteria that need to be satisfied, the interpretation is difficult. It should be easy - did he get smacked in the head or neck, to the point where he wouldn't have done that deliberately to himself?
This can be applied to pretty much any rule that looks to have a grey area. If players at the front of marking contests are throwing themselves forward, putting mustard on it, looking for a push in the back, you're probably paying too many push in the backs. If players aren't taking contested marks anymore, maybe you're too lenient with holding in the marking contest, or with chopping the arms. If players keep opting to take on the tackle, and often drop the ball creating an overly congested rolling maul, maybe you're too lenient on dropping the ball. If players are being slightly held after they get rid of it, and they throw their arms in the air and fall down onto the ground, "acting", then maybe you're paying too many holding the man free kicks.
Incentives would also work for skills, i.e. goal kicking accuracy, but that's another post...