It is your responsibility to obtain necessary visa to enter the UK to attend the Games. As the LOC is unable to refund registration costs outside the cancellation periods, it is advisable to confirm visas as soon as possible. All team members should apply in good time to obtain visas – the earliest you can apply for a visa is 3 months before travel. Visa support letters to be requested via firstname.lastname@example.org
This link will help athletes and family members to check if they need a visa to travel to the UK, with a helpful step by step procedure. The standard visit visa rules will allow visitors to participate in sports events. This Home Office page explains what a visitor can and cannot do.