When people dial a gate, they generally enter from the 'front' of the stargate. For convenience's sake on most planets, the 'front' of the gate is defined as the end that faces toward the DHD. Its also the side that has the 'kawoosh' splash out effect.
Even when 'space gates' were introduced in Atlantis, we get treated to a scene where some darts are guarding a gate, from only one side:
But what happens if an object entered from the 'back' (i.e., the other side) of an active gate?
Note: I'm not talking about incoming/outgoing directions. I'm assuming a "we dialed out, now we're gonna walk around the gate and enter from the wrong side" scenario.