this is what someone posted on a fbook post about why they brake check
. First the initial "accident" is part of a game they play. They ride in a huge group and will operate together to slow down traffic. Next they pick out high end vehicles targeting people with families in them, the targets will usually be white or Asian. Then one of the riders will do a "brake check" and stop suddenly in front of the target vehicle causing a minor bump. In some cases they will just roll back into their target vehicle. They will then mob the vehicle demanding money and or begin attacking the person inside. It is their practice to also slash the tires to prevent the vehicle from escaping. Truckers are well aware of them and are advised not to stop. You can clearly see in the video how they are well practiced in this style of attack.
Fyi, the biker who was in a coma, his licence to drive was revoked in 1999, and been driving illegally since then with multiple traffic violations.