How to airsuck and deal with airsuck?

As you know, pyros have the ability to airblast, or push things away with a jet of compressed air for 20 ammo. You might not know that sometimes you can apparently use a jet of compressed air to suck fleeing spies into the Pyro.

What's going on? Is airblast behaviour wonky if a player is too close to the pyro? Is the pyro just airblasting me obliquely into a wall and somehow the game won't push me back if that happens? Is it just netcode wonkyness? How do I get out of this situation?

Pyros do not have the capability to "air suck". However, if the spy cooperates/is disoriented, you can airblast them straight up into the air while you're running forward. This would give the illusion that they're being sucked toward you.

Part of TF2 physics is a concept called air strafing. It's commonly and most obvious with rocket jumping soldiers and sticky jumping demos, however can also be done with airblasts. If a spy attempts to air strafe when you airblast him, he can successfully stay pretty much in place. Since your airblast does not receive extra force moving forward, it can appear as though you're sucking them towards you.

Air strafing is a common tactic to avoid getting airblasted off a cliff. Instead of holding W, hold A or D while facing parallel to the cliff.

Another thing that might be happening, if you're not being lifted into the air, is that Pyros have the ability to airblast you into the ground, which will temporarily hold you in place long enough for them to catch up and burn you to a crisp.