(Clarification - when I say football I mean soccer unless otherwise specified.)
Hey, great question.
Here's some thoughts on basic rules and questions which might help you design an interesting game.
What are the unique rules of the world?
Any game inherent to the world you're building should ideally seek to incorporate the rules of the world. The idea (if your story is set in a different world from ours) is that there is something unique in your world that led to the development of this sport. The beauty of quidditch is not that it is a magical game loved by the wizards, the beauty of the game lies in the fact that it is a normal game which makes complete sense for the rules that govern the world of wizards, yet it remains fascinating to us muggles.
Any game would be far more thrilling (to write and read) if it had flying broomsticks. Find the flying broomsticks of your world and incorporate them into the sport.
Watch a full length football match. There are moments where you're excited and there are moments where you're not. When do people get excited in a football match?
When the ball nears the goal post? Will they score? Will Messi slide one in? Feel that thrill. When a player pulls off a ridiculous move? Notice the awe.
Sport is popular because it creates moments of excitement and conflict. But how those moments are created depends on the sport. Some observations in this behalf:
Football relies on fleeting moments, but man when things happen its crazy. You wait and wait and wait and then someone comes close or scores and its all madness.
Basketball has these moments occuring more frequently, but with lesser payoff unless something absolutely spectacular happens.
An interesting sport in terms of Thrill creation is Cricket (not unlike baseball in some structural terms). The game is broken into segments called overs, where a small red ball is hurled six times by a bowler to a man holding a wooden bat, trying to ensure he doesn't get out and score the most amount of runs possible in those six turns (a *very** general idea of the game). There are eleven members in a team but there is always a bowler vs. batsman situation happening. The game can be tediously slow, but there are times when the very nature of the contest within a contest (individual battle nested in a team battle) is riveting stuff.
What kind of thrill do you want to create? Slowly built up tension like cricket? Random but exhilarating adrenaline like football? Or steady but rewarding fun like basketball?
When you say Physical sport, how physical do you mean?
Usually - usually - the more intimate and physical a sport is, the more exciting it is to watch. A more physical sport will also make you wince more, may hurt your sensitivities, and may not be for everyone. Then again look at American football or ice hockey. They are very physical and aggressive by design, and the prospect of physical injury adds a layer of tension to proceedings.
With the advantage of the sport being fictional, it can range from being gladiatorial combat based - where one might die, to just knocking around a weightless shuttlecock like in badminton - where changes of a brutal injury are not as high. A general rule appears to be - higher the physical danger, the more tension it'll create, leading to more fun reading and writing.
Some things to ponder in this regard are:
Is your sport going to hurt? How much and how often? Is death possible?
Some examples of Great Fictional and Real Sports worth your Attention
The bending tournament in Avatar: Legend of Korra is without contest my favorite fictional sport. It blends action, tension and worldbuilding perfectly.
It is a two team sport. There are three participants in every team with a demarcated area that is their own. Each team must use martial arts and bending (air/water/earth/fire) to push out the other team from their zone while dodging the oppositions attacks.
Quidditch is something already addressed in the question, and is fantastic. Real danger, high speed, major thrill moments.
A real sport I think you should check out is Pro Kabaddi League. It is a smaller version of kabaddi, with limited room, and makes for some awesome moments of raw physicality, cleverness and fun. A lot of inspiration for creation of new alternatives there.
BONUS FOOD FOR THOUGHT FOR THE WRITING PART
How inherent to the plot is the sport? (or how complex can you make it?)
If your story is a sports underdog story in a secondary fantasy world, well firstly, awesome idea! Secondly, you have open license to complicate the sport and make it as interesting and intriguing as possible. Put another way, if the sport itself is inherent to the plot, you can reveal all the nuances of the game at leisure to the reader.
If it is just throw-away worldbuilding which you may or may not utilize at a later point in the story, well, don't spend too much time explaining it just yet. A good example of this is Nine Kings from the Lightbringer trilogy by Brent Weeks. In the Black Prism (the first book) he merely references the game because it is practically of no relevance to the book. By the second book, its slightly (but not yet enormously) important to the plot so he slowly starts weaving in references and rules. In the second book, we see plenty of games of Nine Kings but the rules are only explained towards the end and even then partially. By the third book, this game (and the cards involved) become essential to the plot and suddenly, we know a lot more about the nature of the game, the cards, the rules etc. I get that Nine-kings is not a physical team sport, but the lesson for exposition remains the same IMO.
In conclusion, know if you're writing a magical Mighty Ducks story or something more akin to the Lightbringer trilogy.