We never really covered this in the rule book, but it has come up from time to time. What happens if a character with Melee 2 [Swords 3 (Long Sword 4)] picks up a sword-style weapon that he has never experienced before? Well, if he really has no knowledge of this weapon, he would suffer the non-skilled modifier, but since it is a sword, he still gets the MEL and SWD group skills. Huh? Yep - If a knight who has practiced with only straight edged weapons his whole life picks up a curved scimitar on the battlefield, he would have +10 (MEL) +15 (SWD) -15 (non-skilled) for a net +10. Now, give him a couple hours to practice with it and that modifier might go away.
So, is this just another chance for GMs to mess with their players? No. It is intended to stop standard soldiers from picking up exotic weapons and using them as though they were born with one in their crib. Furthermore, hopefully it never happens, but a medieval knight should not be able to pick up a light saber and use it with skill. He’d fumble around with it, maybe finding a way to use it as a sword, but definitely not look like a Jedi. With such an extremely different weapon, it might take a few days of training for him to lose his non-skilled modifier. Anyway - some things are beyond the scope of group skills until the character actually encounters them and recognizes them as something familiar. (If the knight can’t figure out how to turn the light saber on, it really doesn’t matter what he might be able to do with it.)