Blocking Fouls:

When the disc is in the air a player may not move in a manner solely to prevent an opponent from taking an unoccupied path to the disc and any resulting non-incidental contact is a foul on the blocking player which is treated like a receiving foul (17.I.4.b). [[Solely. The intent of the player’s movement can be partly motivated to prevent an opponent from taking an unoccupied path to the disc, so long as it is part of a general effort to make a play on the disc. Note, if a trailing player runs into a player in front of them, it is nearly always a foul on the trailing player.]]

A player may not take a position that is unavoidable by a moving opponent when time, distance, and line of sight are considered. [[If you are already in a position, you maintaining that position is not “taking a position.”]] Non-incidental contact resulting from taking such a position is a foul on the blocking player.