1) McGrath steps on a cricket ball

Australians wishing to hush the buzz of your average Pom (read: most Australians) will never tire of pointing out the only two Tests England won in the 2005 Ashes were the ones Glenn McGrath missed.

Having merrily helped himself to nine wickets in the first Test, McGrath was tossing a rugby ball around with the reserve wicketkeeper Brad Haddin before the second Test at Edgbaston. Haddin threw an errant, bouncing pass, McGrath turned to pick it up, stepped on a nearby cricket ball and bang went the ligaments in his right ankle. Michael Kasprowicz was drafted in, Ricky Ponting won the toss and chose to bowl, Michael Vaughan tried to keep a straight face … and you know the rest.

Had McGrath played, would England have been allowed to score 407 on that first day? Would they have lost that Test, with it almost certainly the series, and the course of English cricket in the 2000s altered? What would that have meant for Kevin Pietersen’s career? Might England have actually won the game sooner without the dramatic finish, if it was the notoriously terrible tail-ender McGrath in on that final morning instead of Kasprowicz? Who knows, but for England supporters it does not bear thinking about.

2) Women’s football is banned

In the years after the first world war, women’s football was pulling crowds north of 50,000, with players such as Lily Parr and Bella Reay the stars of a burgeoning movement that looked as if it would run parallel to the men. But in 1921 the Football Association, showing the sort of forward-thinking and liberal attitudes it would stick by for years to come, decided the number of people flocking to watch the women could threaten the men, and that it simply was not on. It declared it was its “strong opinion the game of football is quite unsuitable for females and ought not to be encouraged”, and banned it from its grounds.

A few clubs – most notably Dick, Kerr Ladies – soldiered on but most disbanded and the women’s game became disparate and uncoordinated, forced to play in parks, snuffed out by the most basic sexism.

By the time the ban was lifted in 1971, the women’s game had 50 years to make up on the men, broadly explaining why it is still catching up in terms of popularity, funding and prominence, at a time when the men’s game is awash with money, attention and fame. Where might it be now without those lost generations?

3) Seles is stabbed

Monica Seles was a teenager when she won her eighth grand slam title. In seven majors between 1991-93, she lost one match. She had a legitimate chance to beat Margaret Court’s record of 24 by her mid-20s. In three of Seles’s major finals, she beat Steffi Graf. But during a tournament in Hamburg, shortly after Seles won the 1993 Australian Open, obsessed Graf fan Günter Parche invaded the court and plunged a knife into her back.

The physical wounds healed fairly quickly but the psychological ones (combined with her father being diagnosed with terminal cancer) caused her to miss more than two years and 10 grand slam tournaments. Graf won the next four grand slam titles following the stabbing, and a further seven after that. Tennis was denied a potential decade-long rivalry to rival Navratilova-Evert.

“I had grown up on a tennis court – it was where I felt most safe, secure – and that day everything was taken away from me,” Seles told the Guardian in 2009, but she said she tried not to think too much about what her career might have looked like. “I would have gone crazy a long while ago if I had done that.”

4) Big Sam’s pint of wine

If Sam Allardyce had turned down a flagon of chardonnay with some so-called businessmen who turned out to work for the Daily Telegraph, and therefore not been forced to step down as England manager, there are so many different paths down which the team could have gone.

Would Allardyce have been as quietly ruthless about calling time on Wayne Rooney’s international career as Gareth Southgate was? Would he have been so tactically imaginative? Would he have sorted England’s ticker, penalty shootout-wise?

But this is not even really about on-pitch matters. England would probably still have qualified for the World Cup, and given the path they had in Russia might still have reached the semi-finals. But it feels as if the other stuff that has changed is more important.

Would Allardyce, for example, have so elegantly invited Boris Johnson to do one? Would Allardyce have spoken out so firmly against racism? Would he have fostered such a positive atmosphere around the England team, making people … like them again? As a consequence of that, would Declan Rice have been so keen to declare for England? And where would the waistcoat industry be?

5) Brady steps in for Bledsoe

In 2001 the New England Patriots were keen to tie their starting quarterback down to a new contract. Over the previous eight years he had been one of the NFL’s best, and his backup was an unremarkable kid taken as the 199th pick in the previous year’s draft. So keen were they, that Drew Bledsoe was given a 10-year, $103m contract, then the biggest ever signed in the NFL.

But in the second game of the season, Bledsoe sustained an injury that almost killed him. A brutal hit by the New York Jets linebacker Mo Lewis initially seemed to have merely concussed Bledsoe, but it was later discovered a blood vessel was severed in his chest, causing internal bleeding. Doctors removed about four litres of blood from his chest cavity.

Bledsoe’s replacement did a pretty good job. Tom Brady led the Patriots to their first Super Bowl win that year, then another five since, and is regarded as the greatest quarterback ever. Bledsoe was traded the following summer to the Buffalo Bills and, while he did fairly well individually, never made another Super Bowl.

Don’t cry your eyes out for Bledsoe, mind. These days he is running an award-winning vineyard in Washington state, and it sounds as if he is having a very pleasant retirement.

6) Ferguson and Abramovich do not choose Tottenham

Are Tottenham the biggest “what if?” club in football? There are so many stories about misfortunes that have befallen them, or things that could have gone the other way, but the biggest two involved arguably the two most influential figures in the first 15 years of the Premier League.

The extent of Roman Abramovich’s interest in buying Tottenham in 2003 may never be truly known, unless the notoriously taciturn oligarch suddenly starts spilling beans. But he certainly had a meeting with Daniel Levy and, according to The Club, a recent book by Joshua Robinson and Jonathan Clegg, decided against taking things further after declaring Tottenham High Road was “worse than Omsk” in Siberia. The Fulham Broadway shopping centre near Stamford Bridge was clearly more to his tastes.

But Spurs might not have needed a super-wealthy backer to become a dominant force in English football had Sir Alex Ferguson kept his word in 1984. According to the then chairman Irving Scholar, Ferguson shook on a deal to take over from Keith Burkinshaw, but reneged on it for reasons unexplained, staying at Aberdeen before joining Manchester United two years later.