Nine former rugby union players have begun a legal process against English and Welsh rugby union authorities and World Rugby, saying the sport has left them with permanent brain damage.

Global governing body World Rugby and the Rugby Football Union (RFU) say they take "player safety very seriously". The Welsh Rugby Union (WRU) say it "supported and endorsed the World Rugby comment on the subject".

But the sport's authorities are once again having to address safety concerns at all levels of the game.

The BBC's rugby union correspondent Chris Jones answers some of the key questions the sport now faces...

What are the current concussion rules in professional/elite rugby?

Any player showing clear signs of concussion, or suspected concussion, must be removed from the field of play without returning. However, in the event of head contact where the prognosis is not clear, a player will undergo an off-field head injury assessment (HIA). A player can be temporarily replaced while the HIA is being conducted. The HIA was adopted into law in 2015 and was extended from 10 minutes to 12 minutes at the end of 2019.

Following a concussion, every player must go through the graduated return to play (GRTP) process, whereby the participant undertakes a phased return to exercise and contact before being cleared to play again. While a player is technically able to play within six days of suffering a concussion, they can only start the GRTP steps when they are symptom-free.

Do the same rules apply for amateur and children's rugby?

No. There are no HIAs at community level, and no HIAs in the women's Premier 15s. Any player suffering a concussion or suspected concussion must be permanently removed from the field of play, with the governing bodies urging the amateur levels of the game to abide by the motto: "If in doubt, sit them out."

After suffering a concussion or suspected concussion, all adult amateur players are advised to have a period of at least one week of physical rest before starting the GRTP protocols. This is mandatory unless the player has accessed an "advanced level of concussion care".

Anyone under the age of 18 must rest for a minimum of two weeks before starting the GRTP.

What changes/improvements have been made in recent years to address concussion concerns?

As well as the introduction of the HIA and GRTP protocols, preventing, identifying and treating concussion has been a major focus of the governing bodies for the past five years or so.

Independent match-day doctors and pitch-side concussion spotters are two of many recent developments when it comes to identifying and treating concussion, while the rugby law-makers have also passed a series of measures to crack down on high and dangerous tackles. New laws were introduced in January 2017, while in May 2019 the high-tackle framework was published, designed to achieve consistency in the officiating of high tackles and to protect players' heads, with red and yellow cards issued as a deterrent and to change the behaviour of the tackler.

However, while advancements have certainly been made over the past decade, the legal case will examine whether the authorities historically failed - on the balance of probabilities - in their duty of care to players. While there is no doubt the authorities have woken up to the dangers in recent times, did they move quickly enough? Did they do all they could with the available evidence, or did they ignore the warning signs?

Have those changes proved successful so far?

The 2019 tournament was the first Rugby World Cup to feature the high-tackle sanction framework, with World Rugby subsequently reporting a fall in the incidence of concussion compared with elite competition averages in 2018.

Meanwhile, the introduction of the HIA has resulted in many more players with concussion being identified and therefore removed from the field.

However, the system and the implementation of it has not been without controversy, while leading experts in concussion and brain trauma have also criticised the RFU's reluctance to acknowledge a link between concussion and Chronic Traumatic Encephalopathy (CTE), with the union saying firm evidence has yet to emerge.

The game has also been grappling with the unintended consequences of various law changes and player welfare initiatives. For example, a high-tackle trial was abandoned in the RFU Championship Cup, with the banning of tackles above the armpits actually resulting in a higher number of concussions.

What further discussions have there been on changes in the future?

In August 2019, World Rugby approved a series of law trials as part of its vision to make the sport "simpler and safer".

Aside from law alterations, numerous other changes to the game have been touted, such as reducing the number of replacements to increase fatigue and therefore free up space, an idea being actively explored by World Rugby.

England head coach Eddie Jones has also revealed the game's authorities are considering banning tackling above the waist for any player under the age of 12, to encourage and develop safe technique from an early age.

Numerous former players have also called for a limit in the amount of contact training done in the week, as has been the case in the NFL, with the group of players who are bringing the legal action drawing up their '15 commandments' which they feel could make the sport "85% safer".

Is there a real possibility that the sport could change dramatically - and what changes could there be?

Given the severity of the latest developments, rugby is at a crossroads. Completely eliminating risk in a contact sport is unfeasible, but the game's authorities need to strike a delicate balance between making the game as safe as possible while preserving the sport's uniqueness. Furthermore, while player welfare in 2020 is much more of a priority that it once was, the players are also bigger, faster and stronger, with the emphasis on "winning collisions" greater than ever.

The laws at the scrum, the breakdown and around the tackle height are all under constant review, while the boss of the RFU acknowledged this week the union needs to reassure parents the game is safe for their children to play: "We have got to make sure families feel comfortable taking their kids to minis and juniors to continue playing the game," Bill Sweeney told the BBC.

More research into the prevention and treatment of concussion among women and girls is also needed, with female participation a huge area of growth in the game recently.

How much is rugby viewed as an example for other sports to follow?

Compared with the other major sports in the UK, such as football and cricket, rugby union's management and education around concussion has led the way. However, given the level of physical contact in the sport, this is to be expected.

But, to reiterate, this legal case will not hinge on what is being done now; it will hinge on what was done - or not done - back when Steve Thompson, Alix Popham and Michael Lipman were playing. Although with Adam Hughes coming forward at just the age of 30, having retired as recently as 2018, the governing bodies may also be challenged on how they have managed concussion and brain injury much more recently.