Definition of post up:
(v) :
To enter any information, data etc (into a register, account, record etc).
(v) :
To affix a notice, announcement etc, to a post, board, wall or the like.
(v) :
(basketball) To establish a position in the frontcourt on one side or the other of the free-throw lane, especially used against smaller defenders.
(v) :
To occupy a position.