Hmm as far as I know and tested, the only things that the sandman hits are the balls that come with the sandman package, and enemy players that are stupid enough to run into your taunt.
The achievement is indeed to pick up a ball that's separated from an enemy scout, picked up and launched back. though pyro's can indeed blow back the ball with compression blast and if done without ball hitting a wall/floor or a player that's too close to you, you can indeed return the stun.
The Sandman won't hit back balls that are flying towards you, I tested that thoroughly and nothing out of a well over 150 balls were returned to sender.
and as for stickies.... Not tried that, and not going to... I do not have a friggin deathwish!
Pipebombs go ''boom'' on impact with an enemy so that'd be a no, and a sticky... well... usually says boom as soon as it's ready to be triggered, the more since a scout will be standing under the sticky rain.
So I don't think you'd have to try, it's impossible for all I know and care... too risky to try (but that's me)
If I find myself online, bored and with a friend online, I might give it a go, who knows what I find out. Will report any spectacular discoveries, but nothing guaranteed.





