Good question, and some good answers so far.
I will confine my remarks to what are sometimes called invasion games: the sort of sports that have a pitch, two teams, and a ball (or a non-ball like a puck or frisbee). Yes there are other good sports like archery or combat sports or rounders, but I won't talk about them.
Think about possessions, chances/shots, and goals
In the short term, you want to have possession.
Once you've got possession, you want to build up to a shot. You try to move the ball into a threatening position by passing (which is vulnerable to interception) and dribbling (vulnerable to tackling).
Once you take a shot, you want it to score
All of these should be very error-prone. None should succeed anything close to 100% of the time.
Point 1 relates to dribbling versus tackling (and passing versus intercepting); possession should be precarious.
Point 2 relates to territory; you should need to fight to win territory.
Point 3 is commonly seen in any sport: players miss some shots, get some.
Balance dribbling and tackling
Dribbling and tackling are universal: one team possesses the ball; the other tries to take it from them. These need to be in balance.
When in possession of the ball, you should have it under control, BUT not too much control; the opposition should have a chance to take it from you. Any well-designed sport will have this.
Soccer is brilliant because it has one main rule (it has lots of rules, but one main rule) and that's don't use your hands. Once you have this rule, it follows that the ball will never be under ABSOLUTE control (except when it's in the goalkeeper's gloves) and the tackling and dribbling methods are obvious. Basketball also has a simple rule (you gotsta bounce it) to limit the amount of ball-control and give tacklers an opportunity. Field hockey too: the nature of the game means the ball is under control, but not too much control, and the tackler can get it.
If you DO allow a player to hug and hold the ball and run with it, THEN you must allow the most intense form of tackle: this is what rugby does. (Rugby doesn't use the word 'dribbling' for running with the ball, but it's the same thing.)
At the risk of making lacrosse fans angry, a flaw in that sport is that a player with the ball can run anywhere and it's hard to tackle them.
Balance the importance of territory
Gaining territory should be important, but not all-important.
In soccer, you could in theory score from far away, but in practice you're not gonna, so you've got to get close to score. When footballers do score from far away, it's spectacular because they accomplished the feat of a goal without the important asset of territory. (87% of goals are from inside the box according to the paper with DOI 10.1080/24748668.2011.11868563)
Rugby and American football have field goals (score from a distance) and tries/touchdowns (score by winning territory) and balance between them. (Awarding points for a try/touchdown is awarding points for territory alone, unlike soccer where only territory+shooting gets awarded.)
In 2020-2023, there is a bit of kerfuffle in the hurling community because territory is too unimportant: it is too easy to score from far out, and this makes creating attacks and winning ground unnecessary and sucks a lot of the fun out of the sport. Some want a rule-change to incentivise the "team to push on and keep going for goals and keep trying to create goal chances"
Balance bunching with spaciousness
In soccer, you often run away from the ball into space, then call for the pass.
Consider rugby: the forwards generally run towards the ball and bind together. The backs generally run away into space BUT they are restricted on how much space they can use by the no-forward-pass rule. The no-forward-pass rule essentially means they can only exploit space in one dimension (laterally). In American football (rugby without the no-forward-pass rule) they can run forwards and exploit forward space.
A very spacious sport will move by passing, and dispute possession by intercepting passes. A very bunched-up sport will move by running/dribbling, and dispute possession by tackling.
The size of the pitch affects this (and ratio of the number of players to size of pitch). Aussie Rules has a huge pitch, and as a result possession changes very often by interception. The pitch is too big to run; you must pass. Basketball is about passing, but balanced by having a small pitch with (let me check...) 84m² of court per player, compared to about 971m² per player in Aussie Rules.
Balance shooting with missing
Some sports have a goalkeeper (hockey, soccer, etc.), reducing the success-rate of shooting, and some don't (basketball, rugby, Aussie rules). (To point out an obvious correlation: games with rectangular goals on the ground tend to have keepers; games with aerial goals tend not to. This might change if your players could fly.)
There might be ways of increasing the goalkeeper's power relative to the shooter, e.g. by equipping him with some sort of shield. In ice-hockey, lacrosse, and hurling, the goalkeeper has a bigger stick for this reason. Tweaking the size would tweak the success-rate of shooting.
Basketball makes shooting hard in a very simple way: making the goal small.
Beach handball rules specify that the attacker can't be within 6m of the end.
Aussie Rules has an interesting balance where missing generally is rewarded. A missed kicked (unless massively missed) is awarded ⅙ as much as a good kick. This is small enough they look sad after it; if a bad kick got ½ the points of a good kick, the incentive to kick well would be too small.
Balance stopping and going
The game should flow, the players should play on without the referee's whistle going too often. American football has far too much stopping.
I'd say a flaw in soccer, wonderful as soccer is, is that the offside rule is a bit annoying because it stops the fun. Yes it's there for a good reason, but it's a bit annoying; it's a trade-off.
On the other hand, sometimes you want some stopping to slow down the pace. An exciting sport, like exciting music or exciting sex, will have fast/frenetic spells and slow spells. This is also required by the nature of the human body: we sprint, get tired, rest again, sprint again. Aussie rules is a great example of this: sometimes teams play for marks to make things slow and methodical, and sometimes they run with the ball and handball it and it's fast and chaotic.
I've said above that the aims are to get possession, get it into the danger zone, and create shots. Think about how infringements are punished in all invasion games: play is stopped and the opposition is given those things: possession and sometimes a shot on goal.
funnier
means something is more funny (like a joke), not more fun. You should just sayTennis is more fun than squash
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