I had an interesting scenario come up at a Hyperspace Trial last weekend.
Going into round 5 I was 4-0 with 1st place MOV about 200pts ahead of my nearest competitor. I got paired down vs a 3-1 that needed to win to make the cut. We played the match out and I was winning solidly. I had most of the opposing ships destroyed as time approached. Would it be ethical for me to concede the match right before the end, but after destroying a significant portion of his forces?
Other relevant Info:
In this particular situation I felt my list had a solid matchup vs his and could win a rematch. Given my MOV and record I would seed second and my round 5 opponents would seed near the bottom of the cut. (I can't say that a rematch would have been guaranteed, but certainly possible)
Would this change if my round 5 opponent was a friend?
In all cases assume that none of this was discussed with my opponent.