To block a following rider by moving the back wheel to the side.
elbowing or movement of the wheel that prevents the progress of another one cyclist, generally illegal.
To suddenly move one's back wheel to the side, forcing the following rider to slowdown to avoid running into the front rider's bike.
When one rider, either on purpose or by accident, uses his rear wheel to hit the front wheel of the rider behind him/her.
To suddenly move ones back wheel to the side, forcing the following rider to slow down to avoid running into it.