For those not familiar with the game, could you post a link to the rules?
Pawns can move in either direction, so the situation in your question can only happen if you manage to form a solid line of pawns with a cap on the opponent's side, while at the same time having nothing else left on your side. It's technically possible, but it shouldn't happen unless both players are playing deliberately to force it.
Oh, apparently I could have moved my own pawns *backward*. I had not considered this.