If you are talking about overwatch like in Xcom then it looks like this was a design decision. Not sure I agree with it but haven't spent enough time with the game to know for sure.
'MrMooEar [developer] Nov 11, 2014 @ 1:58pm
I love XCOM! Can you tell?
We talked about it a lot early in development. Does a tactics game need overwatch? We're inspired by a lof of other tactics games like Final Fantasy Tactics and Fire Emblem. These games (and a lot of others!) don't have an Overwatch mechanic. So we decided to leave it on the sidelines when designing the game.
Hopefully that helps! We really don't feel like it's a necessary feature for this kind of game, even though it's super cool and works really well for XCOM. !'
http://steamcommunity.com/app/246110/discussions/0/613941122865394513/
Having already twenty hours into the game, overwatch would have added an extra layer of strategy. You'll find that alchemists are especially hurt by this limitation, but overall being able to set up the field and letting the enemies come to you could have been a viable tactic. Instead, you sometimes need to rush in before they get you, and hope there aren't more enemies lurking in the fog. Or really abuse the hunter's stealth ability.