[PvK]

It's usually not a great idea, since they don't do anything much except possibly get shot. However I think there may be a few ways for it to happen:

1) Tactical combat, human player uses Launch Units during combat.

2) Mines are laid and enemy ships entire while non-aggression treaty is disarming them. Then treaty is broken and combat ensues without any new enemy movement into the minefield.

3) Enemies are in the same sector at the start of a strategic turn, either because they didn't kill each other off during the previous turn due to insufficient violence, strategies used, intervening terrain, cloaking devices, whatever. One or both players then give strategic-level orders to lay mines. Combat then ensues before anyone new moves into the sector and sets off the mines.

PvK