The Australian Open authorities, fresh from the Novak Djokovic saga, banned T-shirts featuring the question "Where is Peng Shuai?" Peng had accused a senior Chinese government official of sexual assault.

Security officers and Victoria Police inside the venue told several spectators to remove the T-shirts, and confiscated banners with a similar message. The officers explained that political and commercial statements of any kind were not permitted under the official ticketing conditions. Those conditions prohibit any "unauthorised promotional, commercial, political, religious or offensive items of whatever nature, including clothing, banners, signs, symbols, leaflets, stickers or flyers". Wow!

The Australian Open makes a whole course in Australian politics. It offers perspectives on gender, sexuality, race, disability, money, lobbying, social movements, and much more. In the recent past it has tried to navigate the politics surrounding the opposition of the great tennis champion, Margaret Court, to gay rights and same-sex marriage.

The event itself has just run a Pride Day to support inclusiveness. It inaugurated a First Nations Day, building recognition of Indigenous rights around the world No.1, Ash Barty. Quad tennis champion Dylan Alcott, Australian of the Year, promotes disability rights. Promotion of social and political causes is widespread in sporting events.

Sporting organisers don't object to politics as such, and I don't think they should; but they want to control the politics. Displays of nationalism are allowed, even though loud chanting and flag waving can be offensive to many other spectators. They are encouraged by officialdom, even when they descend into intimidation of players, because they apparently attract viewers to a cauldron-like atmosphere. There would be a popular outcry if these displays were banned.

The T-shirt ban, later rescinded, opened a can of worms, which also applies to other situations. If you visit a venue or buy a ticket to an event anywhere, you would be wise to look at the conditions of entry. Parliament House, for instance, has its own rules, which apply not just to the chamber galleries but to the other parts of the building. I remember being chided for inadvertently wearing a republican T-shirt in the foyer when I dropped in to pick something up. Electioneering and social campaigning can be banned in many places, like public parks and shopping centres.

T-shirts contrast the power of commercial lobbying with the rights of spectators. Sporting events are examples of us and them. T-shirts are commonplace in public spaces and become the "uniform" of the average spectator.

Television audiences see the paying crowd, but apart from homage to special guests, like men's tennis great Rod Laver, there is not much attention to the suited sections. That is where the board members and their special guests hang out, including representatives of big corporations and other sponsors. Their reward is not just prominent signage but the chance to hob-nob with the board over long lunches.

Sponsors are also a big deal for any commercial event like the Australian Open. One of its sponsors is the Chinese Baijiu distillery, Luzhou Laojiao. Its 1573 logo is prominent courtside on the major arenas. This official paid relationship contrasted with the silencing of the unofficial Peng Shuai T-shirts.

Tennis Australia has also recently abruptly ended, after one year, a five-year deal with the Australian mining company Santos, whose management is a leading advocate of fossil fuels. The deal had been opposed by climate action lobby group 350.org, which launched a petition to "Tell the Australian Open to say No to Santos". Both these examples show sponsorship is inevitably highly political.

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When people power confronts financial power, it doesn't always win. But it can be highly effective. The authorities initially misjudged wider reaction to the banning of the Peng Shuai T-shirt. Whatever the rules, they must be applied sensitively. There was an international backlash from prominent figures, including former tennis great, Martina Navratilova. Australia again looked bad.

Censorship often rebounds, and this looks likely on this occasion. There is a lesson for community and political leaders that Australians no longer are passive in the face of official advice that quiet diplomacy behind the scenes is the best way to advocate human rights issues. Players are increasingly political in the face of official pressure; I will be surprised if spectators don't follow suit by respectfully exercising their citizenship rights inside sporting arenas.

Where this will lead is unpredictable. Sport may never be the same. But the cat is out of the bag. It may make us all uncomfortable at times, because we won't like some of the messages on the T-shirts. On some issues there may even be counter-protests by T-shirt.

Free T-shirts will be handed out by protest organisers before the women's final this Saturday. Tennis Australia has changed its policy, realising it was unwise to prevent spectators wearing them inside the stadium. There would certainly have been demonstrations outside - and chanting inside - leading to huge publicity.

Censorship has lost out. I won't be surprised if some players help activist spectators by themselves wearing a Peng Shuai T-shirt. They will be under official pressure not to, but players themselves already have a long history of social and political activism.