How are trades allowed after the trade deadline in MLB?

Question

I undertand it has something to do with clearing waivers, but why wouldnt a team just pick them up off waivers?

Answer 1

Teams' needs change daily. A player may pass through the waiver wire one day, and four days (and one key injury) later, he's the player they need. So timing is involved.

Answer 2

Its all through waivers  

Answer 3

Doesn't work like that after July 31. After that, any player that is traded must either:

clear waivers (all other teams pass on putting in a claim for him) - in which case, he can be dealt to any team (as long as he doesn't have trade restrictions in his contract).

                                    or

be traded to the team lowest in the standings that claimed him. If a claim is made, the two teams have 48 hours to work out a deal. If no deal is reached, no trade is possible. The team that owns the player can either pull him back from waivers, or let him go to the team that claimed him for no compensation.