DeltaOneG |
Overrun just allows you to move through an enemies square. Normally this is not possible.
If they try to resist and fail they're knocked prone. If they succeed you can't move through their square.
All other rules for movement apply (doesn't have to be straight on account of overrun, can't move more than your move allows, can't end your movement in another creatures square, etc.)
Remember that overrun is made as part of a normal move or charge action. Except for the overrun part, the move or charge behave as normal.