The visibility of tennis coaches on the ATP and WTA tours has been growing by leaps and bounds, but at the same time, the top names, as successful as some have been, don't seem to enjoy great job security these days.

Millions of viewers now watch and listen as coaches advise WTA pros during matches. At the US Open, Sascha Bajin -- the coach of Naomi Osaka -- held a heavily attended news conference. Patrick Mouratoglou -- and his actions -- were the object of nearly as much attention as his protege Serena Williams after the US Open controversy in the final.

After 11 seasons, David Witt is out as the coach of Venus Williams. Michael Dodge/Getty Images

"It's great that the game is expanding, and coaching gets more visibility," Kamau Murray, coach of Sloane Stephens, told ESPN.com. "The bigger the show gets, the more revenue it brings in, the better it is for everyone. But we coaches also have to make sure we are playing the appropriate role for our players."

That brings us to the recent upheavals in the coaching ranks, a trend to which Murray was not immune despite having orchestrated Stephens' Grand Slam breakthrough at the 2017 US Open. Just days ago, Stephens announced she and Murray are "on a break" of undefined duration. At almost exactly the same time, Venus Williams -- 38 years old and in danger of falling out of the top 20 -- cut loose her coach of 11 years, David Witt. (Witt told The New York Times that the break came as "a total surprise.")

Then there was Angelique Kerber. She hired veteran coach Wim Fissette late last year to help pull her out of a year-long slump. Kerber won Sydney and Wimbledon, rose to No. 3 in the rankings -- and parted with Fissette days before the season-ending WTA finals began. (Kerber subsequently failed to survive the round-robin portion of that event.)

There were numerous, less-puzzling changes in recent months. ESPN tennis analyst Darren Cahill stepped down as No. 1 Simona Halep's mentor in order to spend more time with his family. In October, Johanna Konta split with Michael Joyce after 10 months (he immediately signed on to coach Eugenie Bouchard). Jim Madrigal jumped from the ATP (where he coached Tennys Sandgren) to work in the coming year with Madison Keys, while Conchita Martinez, Amelie Mauresmo and Marion Bartoli will be in the coaching mix for 2019.

The coaching business is booming, but it's never been more chaotic. The days when player and coach embarked on journey of discovery that sometimes lasted for many years may be a thing of the past. Top coaches like Fissette, Thomas Hogstedt and Sam Sumyk (to name just a few WTA examples) bounce from top player to top player, carrying their trade secrets like tinkers.

"One reason the relationships aren't maybe as long-term is because the entourages of the players has totally changed," according to Sven Groeneveld, who has coached numerous top players, including Maria Sharapova and Caroline Wozniacki, and once led the Adidas high-performance team. "The increases in tournaments and prize money have allowed for bigger teams, so a player can lose a coach now and still have a support team. Also, with former players going into coaching, the players have a larger pool and more opportunity to pick and choose."

Another feature that can undermine a coach is the influence exerted by other individuals in the group. A parent, a significant other, a physio who works his way into the confidence of the player and might not see eye to eye with the coach, or might be eager for a greater share of the credit, can cause problems.

"Anyone in the entourage might have an opinion," Groeneveld said. "Maybe the coach gets all the credit publicly, but behind scenes others may want to claim it."

The decision to fire a coach can be triggered by a great number of reasons, many of them never revealed. As Murray said, there's no HR department to go through, no due diligence required -- and "the boss" (player) is often a 20-year-old with absolute authority.

Despite leading Angelique Kerber to the 2018 Wimbledon crown, Wim Fissette won't be coaching the German star in 2019. GERRY PENNY/EPA-EFE/REX/Shutterstock

But that isn't always a bad thing, at least when a coach hasn't provided good value. As Murray said, "If a player senses that a coach isn't the right fit, or no longer is the right fit, it can take real maturity to call it quits. There are no impediments, either."

Engaging with the press can be risky for a coach. In a far-ranging news conference at the US Open, Bajin said Osaka was sometimes more forthcoming with the press than with him.

"She threw me under the bus in a lot of [news] conferences," he said at the time. "A lot of times I ask her, 'How are you?' She's like, 'I'm good, I'm good.' And then she would be a lot more detailed in her actual press conferences."

Bajin and Osaka seem to have a healthy, open, relaxed relationship. But a more guarded player might not want his or her coach to speak so freely, which is why so many coaches of top players operate under a strict gag order. Some have paid a price for being too open with the press.

"I can remember instances when coaches would give an interview, and it would cause tension between player and coach," Groeneveld said. "But nowadays there are even more angles in which the relationship will be challenged."

One of the most prominent danger zones, many coaches agree, is the pipeline that social media provides from fans and others directly to the players. Almost any Tom, Dick or Harry has a reasonable shot at making his or her voice heard by a star athlete who is active on social media platforms. That might be having a profound influence on young athletes.

"It's so easy to comment on a post or photo or article, and the player will probably see it," Murray said. "People will comment on a [coaching] relationship. Or maybe someone will overreact to a loss. These players, at 21, 22, are not mature enough to block it out, even if they say they are. That has a deteriorating effect. Instead of having two or three voices driving a decision, you can have two or three hundred."

But if all these factors have made life more perilous for coaches, their options have increased dramatically. The rise in the attention they get translates to greater opportunity. Groeneveld, founder of the Orangecoach.com coaching services provider, is happy to see so many former pros flooding the coaching ranks. He said it improves and brings an extra dimension of interest to the game.

The growth of the tour means more coaching job opportunities as well as bigger paychecks. There's no longer any stigma to moving from player to player; some of the most highly regarded coaches are experts at it. In fact, it almost seems as if coaches now function as well-paid consultants, called in to provide a fix over a limited time.

Some coaches have become stars in their own right. Others still shun the limelight. It's hard to say what the appropriate role of a coach is in today's game.

"The WTA is a traveling circus," Murray said. "But the coaches should be an invisible part of show. At the US Open, coaches were too big a part of the show."

It might be true, but for better or worse, they're part of it now.