The PGA Tour's lawyers argued PIF governor Yasir Al-Rumayyan personally recruited players and "played an active role in contract negotiations, and expressly approved each of the player contracts-all while knowing that these deals would interfere with the players' tour contracts".

Al-Rumayyan had argued he and the state-owned investment fund total estimated assets of $620 billion (£515 billion/€579 billion) were protected by "sovereign immunity" and did not need to comply with a subpoena by the PGA Tour's lawyer.

The US District Court for Northern California rejected those claims, and ruled that their conduct fell within the commercial exception to the Foreign Sovereign Immunity Act.

Magistrate judge Susan van Keulen explained the basis for the Court's decision in a 58-page ruling.

"It is plain that PIF is not a mere investor in LIV; it is the moving force behind the founding, funding, oversight and operation of LIV," she wrote.

"PIF's actions are indisputably the type of activities by which a private party engages in trade and traffic or commerce.

"Accordingly, the court concludes that PIF has engaged in commercial activity."

Van Keulen added Al-Rumayyan was "personally involved in and himself carried out many of PIF's activities" related to the operation of the rival league.

LIV Golf had argued that the PIF was a "mere investor".

This decision allows the PGA Tour to seek documents and communication related to matters including LIV Golf's recruiting and negotiating with players and its business plans.

The Court found that the PGA Tour's subpoenas "suffer from overbreadth both in scope and number of requests" and should be narrowed in their scope.

The ruling is expected to be appealed by the PIF and Al-Rumayyan.

A group of 11 LIV Golf rebels including six-time major winner Phil Mickelson of the United States filed an antitrust lawsuit against the PGA Tour in August, but all except Americans Bryson DeChambeau and Peter Uihlein and Australia's Matt Jones have removed themselves as plaintiffs, while LIV Golf has added itself.

They allege the PGA Tour has used monopolistic powers to limit the opportunities of players.

The PGA Tour's countersuit claims that LIV Golf interfered with its contracts with members.

A trial is not expected until January 2024 at the earliest.

The PIF has committed a reported $2 billion (£1.7 billion/€1.9 billion) to LIV Golf in the first two years.

It is one of the PIF's most notable moves into sport, with others including the purchase of English Premier League club Newcastle United, which is chaired by Al-Rumayyan.

Saudi Arabia has also become a destination for several major sports events, including the 2034 Asian Games in Riydah and the 2029 Asian Winter Games in the yet-to-be-built resort of Trojena.

The country was also recently awarded football's 2027 Asian Cup. 

It has held numerous professional boxing fights, is a Formula One Grand Prix host, was recently awarded December's FIFA Club World Cup and is seeking to host the 2030 FIFA World Cup with Egypt and Greece.

This rise has not been without controversy, and critics of the regime of Crown Prince Mohammed bin Salman, the country's de facto leader, have accused Saudi Arabia of sportswashing.

Human rights concerns against the world's leading exporter of crude oil the assassination of Khashoggi, its role in the bombing in Yemen, harsh restrictions in place on women's rights and its use of the death penalty.

American golfers who have joined LIV Golf have faced particular criticism because of alleged Saudi links to the 9/11 terror attacks.

LIV Golf's launched in October 2021, spearheaded by Australia's two-time Open Championship winner Greg Norman, has sparked significant infighting within men's golf.

More than 30 PGA Tour members have been lured to LIV's lucrative tour, including last year's Open winner Cameron Smith of Australia and long-time world number one Dustin Johnson of the US.

LIV Golf's second season is set to begin in Mexico next week, with a further 13 events pllanend, each of which have a $20 million (£16.7 million/€18.7 million) total individual prize fund.

The PGA Tour suspended LIV players for violating its membership regulations, and has responded with increased prize money at "elevated events".

LIV Golf has undergone significant change in recent months, with its chief operating officer, chief marketing officer and chief communications officer all leaving their roles.

Saudi Golf Federation chief executive Majed Al Sorour also stepped down as LIV Golf's managing director.

LIV events are 54-hole competitions played with a shotgun start, and do not currently offer Official World Golf Ranking points used to determine qualification for the Olympic Games.