Thanks to a certain pandemic, the Hong Kong marathon was not held last year. With the pandemic appears to be under control, the event will be held in autumn at a smaller scale (the number of entries allowed is about a quarter of entries for the 2019 event.) The applicants would either have to receive show proof of vaccination or show a negative test before allowed entry on race day. Instead of runners starting the race together, the race start will be staggered, with runners divided into small groups and groups starting minutes apart. (Group assignment would probably be based on the time a runner self-reported time needed to complete the course —.)
The organizers are taking precautions to keep the runners safe from catching COVID. However, the city's zealous (perhaps hysteric is a better description) "patriots" would likely keep close attention to the runners and volunteers for any symbol they consider "threats to national security". One would not be surprised if they proposed the following measures to be implemented to prevent the spread messages they consider threats to national security:
Anyone wearing clothing which contains yellow or black on race day would be denied entry (yellow being the colour of the "treasonists" and black is a symbol of the "black thugs") and handed over to the national security branch of the police. They would be placed in indefinite custody and their bail request would be rejected. If a running wear clothing or hold items containing "subversive" messages or the flag of the Republic of China, they would be treated in the same way. Likewise for any runner with subversive tattoos and body paint or wearing costumes which may offend the "patriots".
Anyone wearing gear made by companies boycotted by Chinese netizens would be denied entry (By wearing such gear, the runner hurts the Chinese people's feelings). (If this rule is in place, the event would have to change its apparel sponsor from Nike to another company.)
The race is open to anyone. However, if a runner is caught talking or non-verbally communicate with a foreign-looking runner/spectator during the race, they would be arrested for colluding foreign forces.
Plainclothes officers will take part in the race to monitor runners for their clothing and belongings in case they are missed by race marshals and volunteers. If officers spot runners wearing items they deem illegal, they will be run the offenders down (no pun intended) and arrest them.
The bib numbers containing any of 1314, 47, 51, 520, 535, 64, 69, 612, 615, 616, 689, 721, 777, 831, 101, 1001, 118, 1108, 1111 (and any other number the powers that be deem "sensitive") would not be issued as such numbers may serve as reminders to events the "patriots" wish the world to forget.
More restrictions on personalized bibs. (The list of restrictions keeps expanding and there is not sufficient room to list them all.)
It is not yet known if spectators would be allowed to cheer runners on along the route. If they are allowed they are subject to the same rules as the runners. In addition, if spectators hold banners which the police considers "subversive" or shout slogans which "hurt the feelings of the Chinese" (such as Heung Gong Yan Ga Yau), they would be arrested on national security charges, put in indefinite custody and their bail request would be rejected.
The above list probably not exhausive (since I don't have the imagination of the "patriots"). To those who wish to enter the race, enjoy the run. However, one may wonder if the only way to safely finish the race without being harassed by the national security zealots is to dress like ancient Olympians. (I don't think that is feasible though, for obvious reasons.)