In response to an unseen cue, the trumpets are raised in unison and blare out a brassy battle-cry.
As one, the visiting team's supporters in the packed stands come to their feet and pound together plastic batons bearing the Chunichi Dragons logo above their heads.
A man in a happy festival coat in the club colours heaves a huge flag into the early evening sky.
Just another noisy and colourful day out for the family at a match in Japan's professional baseball league. But maybe not for much longer.
Concerned that organised crime groups are infiltrating ball parks across Japan, the Pro Baseball Owners' Association has decided to require that from the start of next season, in April, members of the most die-hard fan groups - known as "oendan" or cheering squads - will need a permit to urge their team on from the stands.
Anyone who is too noisy runs the risk of being ejected from the grounds.
"I'd not heard about the new rules," admits a surprised Yukio Ueshima, a restaurant owner and long-time Yokohama Bay Stars fan. "How will they enforce them?"
Supporters may no longer be free
to shout and cheer nosily
Out on the diamond, the Yokohama pitcher has just dismissed the third batsman for the Dragons, who are based in Nagoya, and Ueshima's attention is distracted as he claps and yells at the Bay Stars players to "gambatte" or "give it your best shot."
He might not be allowed to get so raucous in eight months' time.
Ueshima is sitting in the more expensive seats at the Bay Stars' stadium, among younger fans who dream of catching a fly ball and season-ticket holders sipping cold beer, and it is very unlikely that a problem will crop up here.
The new rules, while they will apply throughout the grounds, are clearly aimed at the gangsters in the cheaper sections.
Organised crime groups used to be content with selling black-market tickets on the streets around baseball stadiums until a few years ago.
During the 2003 season, with attendances falling and official tickets easy to come by even on game day, police across Japan began to suspect that team cheering squads had been infiltrated by the gangsters, who had also quickly moved to install themselves as their new leaders.
Soon, groups were taking over whole sections of the stands and politely asking for a donation from anyone whose seat was within that area.
Gangs intimidate or extort to
take over whole sections of seats
Faced with several large men often with the tell-tale signs of the "yakuza", sometimes referred to as the Japanese mafia - tattoos, tight perms that are known as punch perms, or merely the swagger and aggression of the underworld - most either make the contribution or find another seat.
"Clubs were becoming concerned, although it was really something that they didn't want to get too involved in," says Masaaki Nagino, a spokesman for the Central League, one of two leagues that run in parallel throughout the season and the winners of which go on to a national final.
"Gangs are a very touchy issue.
"In the past, the clubs used to rely on the cheering squads to increase attendance," he said. "They were entertaining; they played music, waved the banners and really got the crowd excited, but now it has gone too far.
"They may still call themselves members of the cheer squads, and it's true that during the game they do cheer, but before and after the game there are some who get involved in crimes," he said.
"They pick fights, rough people up and generally cause problems for the clubs.
"And while we don't know exactly why attendance has been falling in the last couple of seasons - it is almost certainly a combination of reasons - this problem is definitely one of them," Nagino believes.
"It's very unfortunate that ordinary people who get involved in these troubling situations may very well never come back to a baseball stadium."
The gangs are blamed in part for
falling spectator numbers
Under the new regulations, all members of cheering squads will have to apply to the club for permission to play their drums or trumpets, wave flags or banners, or even simply chant the name of their favourite player.
Each applicant will be screened for a criminal background and issued a permit that is valid for one season. Anyone subsequently found to have links to underworld groups will have their permit rescinded and troublemakers will be escorted from the grounds.
During the 2004 baseball season, police charged 85 people with offences either inside or close to stadiums, including 38 cases of violence.
For a sport involving half-a-dozen games a night, six nights of the week over six months of the year, the statistics appear startlingly low in comparison with, for example, the troubled 1970s in British football.
"I support any move that will prevent criminal activity at ballparks," says Gary Garland, a writer who has monitored the sport in Japan for many years.
"This isn't all that different from how the British authorities attempted to control soccer gangs and, as there have been occasional problems with 'oendan', new rules have had to be implemented.
"But overall, it won't affect fans who go to the ballpark merely for a good time," he believes. "In fact, it will promote games as safe entertainment.
"Having said that, considering the ties between yakuza groups and the Japanese right wing, it will be interesting to see just how far [the authorities] will go to control gangsters showing up at games, or if this will merely be a one-time sticking plaster," he added.
The fans of Osaka's Hanshin Tigers are perhaps the most notorious in Japanese baseball, although a lot of the problems are more a case of exuberance among supporters of a team that has not had much to cheer about for some years.
Ball clubs are interested in giving
fans a safe environment
A Hanshin victory is traditionally followed by fans leaping off bridges into the filthy Dotonbori canal.
"Organised crime groups have been involved with the Tigers' supporters groups for a while now, and the problem is compounded by the fact that some teams are themselves involved with underworld groups - intentionally or unintentionally - through major supporters such as construction firms," says Jim Allan, baseball correspondent for the Yomiuri newspaper.
"But my feeling is that the authorities want to have more laws on their books than they need, because if the laws are there they can use them in a hurry," he said.
"It will allow the clubs to create a list of fans who are banned and keep them out of ball parks because really, all they want to do is get people to come along to watch a game with the family in complete safety."