Roger Federer suffered a freak knee injury while giving his twin daughters a bath during the January Australian Open and called it a year by July. Rafael Nadal went missing from action after a wrist injury. Maria Sharapova admitted in March that she tested positive for a banned drug and faced suspension. Then Serena and Venus Williams learned their personal medical records with the World Anti-Doping Agency had been hacked -- allegedly by a cyber-warfare group with ties to Sharapova's native Russia.

Then 2016 got even weirder in tennis as the year went on. It's never a good thing for a sport when there's more news made in press releases, news conferences and social media announcements than on the field of play.

But 2016 was a year of drama for men's and women's tennis that saw nearly all of its most enduring stars involved in some sort of turmoil.

Nick Krygios got suspended for tanking a match in Shanghai and was ordered to get therapy, and Novak Djokovic saw his internal gyroscope go haywire due to "private" issues he still has never elaborated on. After winning six titles the first half of the year, including his first French Open, Djokovic won only one event afterward, ripping open his shirts and crying in frustration along the way. Then on Dec. 6, the Serbian star ended his three-year stint with coach Boris Becker, who presided over Djokovic's streak of making nine finals in the past 12 Slams and his two-year stay at No. 1.

Djokovic said they parted amicably. A day later, Becker criticized him in a Sky News interview, saying: "He didn't spend as much time on the practice court in the last six months that he should. Success like this doesn't happen by pushing a button. Success like this doesn't happen by just showing up at a tournament. You have to work your bottom off because your opposition does the same."

Just this past Thursday, yet another reminder of how many hits tennis had to survive as an institution resurfaced: Tennis Australia announced it had hired two more full-time investigators and cut ties with major advertiser William Hill, the sports betting agency, to underline its seriousness about combating the match-fixing and betting issues that surfaced during the Australian Open last January via a BuzzFeed/BBC report.

Despite encouraging results, Nick Kyrgios showed he did little growing up in 2016. AP Photo/Koji Sasahara, File)

That story alleged there has been widespread match-fixing in men's tennis and that authorities in the sport ignored it. The report did not name names but said 16 men who have been ranked in the top 50, including a US Open champion, could be involved. And Djokovic caused a further stir by sharing a story days later about how a member of his team had been approached in 2007 and offered $200,000 if Djokovic would throw a first-round match in St. Petersburg, Russia. Said Djokovic: "It made me feel terrible because I don't want to be anyhow linked to this. For me, that's an act of unsportsmanship, a crime in sport, honestly. I don't support it. I think there is no room for it in any sport."

Sharapova cried foul, too -- albeit for a different reason. In March, she called a news conference in Los Angeles and broke the news herself that she was among the many Eastern European athletes who tested positive for meldonium.

She admitted she had continued taking the drug into February because she was unaware meldonium was newly banned as of Jan. 1. The irony? Sharapova's honesty ruined her chances of getting immediately reinstated a few months later when world doping authorities admitted they didn't fully understand how long meldonium stayed in a person's system.

Many athletes who said nothing were thus allowed to return to competition because WADA couldn't prove they had ingested meldonium before or after it was banned. Sharapova had no such out. She held her tongue during all the back-and-forth as her appeal waited to be heard by the Court of Arbitration for Sport. When her recommended two-year ban by the International Tennis Federation (ITF) was reduced to 15 months by CAS, Sharapova bitterly blasted tennis officials for the heavy price she paid. The former world No. 1 missed the year's last three majors, and was eclipsed by Serena Williams as the top-earning female athlete in the world. Even with the suspension reduction, the 29-year-old Sharapova won't be eligible to play again until just weeks before the start of the French Open in late May. She has promised to return -- with a vengeance.

Victoria Azarenka, who made the surprise announcement in July that she and her boyfriend are expecting their first child by the end of this year, could join Sharapova back on tour around the same time. Azarenka has said she's inspired by the example of Kim Clijsters, who won three Slams after giving birth to her first child.

Taken all together, the 2016 tennis year has been a lot to digest.

But it also has conspired to make 2017 look like it could be one of tennis' most wonderfully unpredictable years in decades after years of hegemony at the top.

And that's not all bad.

Serena owned the No. 1 ranking a record-tying 186 consecutive weeks before Germany's Angelique Kerber overtook her in September while winning the US Open. To understand just how remarkable Williams' run was, consider this: Williams had more title wins (24) than match losses (19) in those three-plus years she stayed No. 1.

And yet, though Williams made the finals of the 2016 Australian and French Open, and won Wimbledon, she played only eight events and 44 singles matches all told -- none of them after September. Her own coach, Patrick Mouratoglou, said Williams had a "bad" year by her standards, even if she was battling shoulder and knee ailments part of the time.

Williams, now 35, wasn't quite as downbeat as Mouratoglou about the big picture. After losing in the semis of the US Open, Williams actually pushed back irritably when a reporter suggested she was too fatigued to win, bristling "I'm a professional" and "If I can't turn around after 24 hours and play again, then I shouldn't be on tour. Fatigue had absolutely nothing to do with it.

"If I was tired, I should definitely get into a new career."

The show of pride was good to see.

Scotland's Andy Murray roared to the No. 1 ranking for the first time by the end of the year, too, when he won the Paris Masters in early November and then quashed Djokovic's attempt to wrest the top spot back. After years of hearing questions about whether he belonged in the Big Four along with Federer, Nadal and Djokovic, the 29-year-old Murray insisted he never really expected to slingshot past them and someday sit atop the world. But he did it, all right, by decisively beating Djokovic at the year-ending ATP Finals in London to become the oldest first-time No. 1 since Australia's John Newcombe accomplished it at age 30 in 1974.

"Unbelievable," Murray said.

Puerto Rico's Monica Puig expressed similar astonishment after she was the surprise winner at the Rio Olympics, giving her country its first gold medal at any Summer Games. Puig beat Garbine Muguruza along the way, the young Spaniard who upset Serena in the French Open final to win her first major.

But from start to finish, the 28-year-old Kerber was the most consistent female player of 2016. She knocked off Williams for the Australian Open title, lost to her in the Wimbledon final and then finished her climb to No. 1 by beating big-serving Karolina Pliskova for the US Open championship after Pliskova upset Williams in a semifinal shocker. Along the way, Kerber admitted frankly that she initially struggled with the heightened expectations that came from winning her first career Slam in Australia, saying, "The pressure after is actually more. Not less."

Monica Puig became the first woman to win a gold medal for Puerto Rico. EPA/BERND THISSEN

But after winning in New York, Kerber insisted she no longer felt out of her depth.

"I think I'm ready, yeah, to have this pressure on my shoulder," Kerber said. "Being No. 1, of course now everybody will try to beat me and have nothing to lose. [But] I will try to take this challenge and try staying as long as I can there."

Argentina's Juan Martin del Potro rivaled Murray and Kerber as the feel-good tennis story of 2016 with some snowballing success in the last half of the year that suggested the wrist problems that plagued him since he won the 2009 US Open -- still his only Slam title -- might finally, blessedly be over.

First, del Potro upset Stan Wawrinka at Wimbledon, then backed it up by beating Djokovic and Nadal in Rio on the way to winning the silver medal. At the US Open a few weeks later, del Potro advanced to the quarterfinals before Wawrinka defeated him in a late-night match in Arthur Ashe Stadium. But the extraordinary scene still had people talking days later. Fans brought del Potro to tears when they began fondly chanting his name near the end of his Wawrinka loss, just to let him know how happy they were to see him back.

From there, it was on to Davis Cup play for del Potro, where he defeated Murray in singles to push Argentina past defending champion Britain in the semifinal round. Then he roared back from a 2-0-set deficit against Croatia's Marin Cilic in Zagreb to spark Argentina's second-day comeback to its first Davis Cup title in five trips to the final. Once again, del Potro cried for joy. What a year it had been.

"I was very close to never playing again," he said, recalling all the setbacks after each of his three wrist surgeries. "And, well, here I am."

That image of del Potro and his teammates celebrating in Croatia as confetti rained down is a nice grace note to linger on heading into 2017.

Federer and Nadal, Djokovic and del Potro, Serena and Sharapova are among the many megastars plotting blockbuster comebacks. If they all return to top form at once, 2017 could be yet another year of fireworks -- but for far happier reasons, and with spectacular results.

"I'm looking forward to it," Kerber said.