TOKYO (AFP) - Former Yomiuri Giants pitcher Shoki Kasahara was arrested on Friday on charges that he helped organise baseball gambling, Tokyo police said, in a scandal which has rocked Japan's leading sport.

The 25-year-old, who has already been banned indefinitely by the sport's governing body, was arrested along with the alleged organiser of a baseball betting scheme, according to a Tokyo police spokesman.

It is the first arrest among the four suspended Giants players accused of being involved in illegal gambling by Nippon Professional Baseball (NPB).

Two of the others - Satoshi Fukuda and Ryuya Matsumoto - also received indefinite bans from the NPB, while Kyosuke Takagi was suspended for one year.

The Tokyo-based Giants, Japan's answer to the New York Yankees, have been fined a total of 15 million yen (S$188,100) over the scandal.

Kasahara is charged with helping alleged gambling organiser Satoshi Saito, 38, by explaining how to bet on professional baseball games and by collecting money from Saito's clients in 2014 and 2015, the police spokesman said.

Before his arrest, Kasahara told NHK television that he had visited underground casinos, but denied betting on Giants games and said he was never involved in match-fixing.

Gambling is generally illegal in Japan and the betting scandal has sent shockwaves through the country's most popular sport at a time when it is bidding for inclusion in the 2020 Tokyo Olympics.

The arrests came after Japanese badminton players, including Olympic medal hope Kento Momota, were booted off the national team for visiting an illegal casino.