I will give you some hints.
It is NOT football.
It is NOT baseball.
And it most certainly is not basketball or hockey!
The number one spectator sport in America is NASCAR.
That is right. Its not even an exercise. Although the drivers do get injured regularly, they're not sports injuries in the normal sense of the word.
Now that isn't to say Nascar drivers don't have to stay fit. They do, but their goal isn't peak fitness - its peak awareness, reflexes and reaction time. In theory a juggler would be good at driving a car in Nascar.
Another big spectator sport is the horse races - again a sport where the rider isn't doing much of the work and its mostly the horse which is getting all the exercise. Horse racing is mostly popular however due to the gambling that goes on, as the horse races really wouldn't exist on a day to day basis without gambling propping it up financially.
Now obviously many people who watch Nascar or go to the horse races are not racing cars around a circular track or riding horses on a regular basis. Many of them have probably never even touched a racecar or a horse.
I am ranting here, I admit.
Sports rants are actually pretty common to sports oriented websites and blogs. There is even a YouTube channel called SportsRantz wherein that is all they do - rant about different sports. See http://www.youtube.com/sportsrantz to see what I am talking about.
Oh sure, some people out there play football, baseball, basketball, hockey, soccer, rugby, cricket... Some of them like me even do boxing, archery and swimming.
But being an avid spectator of a sport and being an active participant in a sport are two extremely different things. They can certainly be complimentary however.
If you watch sports regularly, yes, you can learn things to improve the quality of your performance in your chosen sport. But it will only happen if your chosen sporting franchise is actually giving away professional tips to people new to the sport.
Watch an archery competition on YouTube sometime. They will talk and talk about concentration and focus, and it is true that those things are important. But they will completely skip over important aspects of archery such as form, balance, training regimens, training methodology, diet, cross-training, etc. In other words the sports broadcasters / announcers are really focused on the entertainment value of what they are presenting and they aren't teaching the viewers anything about the sport and how to get better at it.
And there are many televised sports that do this - all entertainment value, almost no sports educational value.
And then there is the advertising commercials - which largely vary between beer commercials and sometimes, if you're lucky, you might get a Nike or Adidas commercial.
Lets take for example the Tour de France - a bicycling race across part of France which takes 21 days to complete and includes 2 rest days. Which means people watching the Tour de France on television are basically watching 21 days of people doing nothing but bicycle really hard (and sometimes have crashes, which admittedly makes it a bit like Nascar, people like to see athletes crashing into each other).
When you watch the Tour de France on television you will see on a regular basis commercials for bicycles. And it is basically the only time I have ever seen a bicycle commercial. You will see other commercials too, again geared towards sports fans, but the bicycle commercials will dominant.
Now that to me is the way commercials for sports SHOULD be done. The advertising fits the sport itself.
Whereas if you watch football every second ad will be either a truck commercial or a beer commercial - because they've recognized that the people who watch football in America are the working class, and they just happen to like beer and trucks. (Ironically you will also see a lot of commercials telling people to not drive while drunk, which makes perfect sense when you consider the other things they are being told to go out and purchase.)
Anyway, back to my original point of this post...
Although I do recommend it be a wall without windows. Breaking windows and losing your tennis balls constantly would be a bad idea.
Some tennis courts also have walls specifically made so people can practice against a wall by themselves - as shown by the image on the above right.
So you definitely don't need a partner all the time if you want to do a competitive sport, and therefore a shortage of an exercise partner should be no deterrent from you getting your needed exercise.
Of course, if you absolutely must have a partner you could also hire me as your personal trainer. Although I admit, I suck at tennis, but that is mostly because my backhand is so horrible and I don't do tennis that often.
However like with any sport that takes patience and practice a person will get better if they just follow the Nike slogan and "JUST DO IT".